ALBERT

Notes: 1 The effects of the immunosuppressants, tacrolimus (FK506) and cyclosporin A (CsA), on catecholamine (CA) release were examined in cultured bovine adrenal chromaffin cells. 2 In intact cells, FK506 (1–30 μm) inhibited CA release stimulated by acetylcholine (ACh; 100 μm), 1,1-dimethyl-4-phenyl-piperazinium (DMPP, 10 μm) or high K+ (40 mm). CsA (1–30 μm) had a little inhibitory effect on the ACh- or DMPP-stimulated CA release, whereas it enhanced the high K+-stimulated CA release. 3 In β-escin-permeabilized cells, FK506 inhibited CA release stimulated by Ca2+ (1 and 10 μm) in the presence and absence of MgATP (2 mm). CsA induced CA release under Ca2+-free condition and enhanced the Ca2+-stimulated CA release in the presence and absence of MgATP. 4 It is known that the Ca2+-dependent exocytosis involves at least two distinct steps, ATP-requiring priming stage and ATP-independent fusion step in adrenal chromaffin cells. Therefore, it is suggested that FK506 inhibits the Ca2+-dependent exocytosis probably at the fusion step whereas CsA induces CA release from bovine adrenal chromaffin cells.

Notes: 1 Prolonged bed rest or exposure to microgravity may cause several alterations in autonomic nervous system response (ANSR). 2 Hindlimb unloading (HU) rats were used as an animal model of simulated microgravity to investigate ANSR changes. The experiments were carried out to investigate the effects of simulated microgravity on the autonomic nervous response of the perfused mesenteric vascular bed (MVB), vas deferens and the colon and duodenum from 2-week HU rats. 3 In MVB preparations of HU rats, the frequency-dependent increases in perfusion pressure with perivascular nerve stimulation (PNS; 8–40 Hz) were inhibited, whereas the noradrenaline (NA) concentration-dependent (1–100 μm) perfusion pressure increases were potentiated. The latter most probably reflected up-regulation of α-adrenergic receptor function. Relaxant responses of NA-precontracted MVB to PNS (4–30 Hz) or isoprenaline were not different between control and HU preparations, while vasodilation induced by the endothelial agonist ACh was reduced. 4 Transmural stimulation (2–40 Hz) induced frequency-dependent twitches of the vas deferens which were reduced in vas deferens of HU rats, while the sensitivity to NA-induced contraction was significantly increased. 5 In the gastroenteric system of HU rat, direct contractile responses to carbachol or tachykinin as well as relaxant or contractile responses to nervous stimulation appeared unchanged both in the proximal colon rings and in duodenal longitudinal strips. 6 In conclusion, HU treatment affects peripheral tissues in which the main contractile mediators are the adrenergic ones such as resistance vessels and vas deferens, probably by reducing the release of neuromediator. This study validates NA signalling impairment as a widespread process in microgravity, which may most dramatically result in the clinical phenotype of orthostatic intolerance.

Notes: 1 This double-blind, cross-over, placebo-controlled study on six healthy male volunteers was designed to evaluate the effects of α2-adrenoceptor antagonism on cardiac parasympathetic regulation. 2 The subjects received atipamezole intravenously as a three-step infusion, which aimed at steady-state serum concentrations of 10, 30 and 90 ng ml−1 at 50-min intervals. 3 Drug effects were assessed with repeated recordings of blood pressure and electrocardiogram, in which the high-frequency (0.15–0.40 Hz) R-R interval variation is supposed to reflect cardiac parasympathetic efferent neuronal activity. 4 At the end of the three steps of the infusion, the mean (±SD) concentrations of atipamezole were 10.5 (3.9), 26.8 (5.6) and 81.3 (21.1) ng ml−1. 5 Within this concentration range, atipamezole appeared to reduce slightly the high-frequency R-R interval fluctuations, indicating a minor vagolytic effect in the heart. 6 Atipamezole increased systolic and diastolic arterial pressure, on average by 20 and 14 mmHg (maxima at the second step of the infusion), which evidently reflects an overall sympathetic augmentation.

Notes: 1 Our previous report showed that in acute cholestasis, the subsensitivity to morphine inhibitory effect on electrical-stimulated contractions develops significantly faster in guinea-pig ileum (GPI) and in mouse vas deferens (MVD) (45.2 and 29.9 times, respectively) compared with non-cholestatic subjects. 2 The possible contribution of α2-adrenoceptor and nitric oxide (NO) pathways on the development of tolerance was assessed in GPI and MVD of cholestatic subjects. 3 Daily administration of naltrexone (20 mg kg−1), yohimbine (5 mg kg−1), and Nω-nitro-l-arginine methyl ester (l-NAME) (3 mg kg−1) to cholestatic animals significantly (P-value 〈 0.05) inhibited the process of subsensitivity in all groups. 4 Consistent with the literature, it was concluded that both the α2-adrenergic system and NO have close interaction with the opioid system and may underlie some of the mechanisms involved in the subsensitivity development to opioids in acute cholestatic states.

Notes: 1 We examined the role of the NO/cyclic GMP (cyclic GMP) pathway in nitric oxide (NO)- and vasoactive intestinal peptide (VIP)-induced relaxation of feline lower oesophageal sphincter (LES). Furthermore, it was studied whether methylene blue, LY83583 and ODQ, which are soluble guanylate cyclase (sGC) inhibitors, could inhibit NO-induced relaxation.2 The nitric oxide synthase (NOS) inhibitor, N-nitro-l-arginine (l-NNA) had no effect in sodium nitropruside (SNP)-induced relaxation, but 3-morpholinosydnonimine-N-ethylcarbamide (SIN-1)-induced relaxation was decreased by the pretreatment of l-NNA, which showed that SIN-1, not SNP, could activate NOS to cause relaxation. Methylene blue and LY83583 did not inhibit the relaxation by SNP and SIN-1. However, the more specific sGC inhibitor ODQ blocked the relaxation induced by NO donors.3 To identify the relationship of NOS, sGC and adenylate cyclase in VIP-induced relaxation, tissue were pretreated with l-NNA and ODQ and SQ22536. These inhibitors produced significant inhibition of this response to VIP. The adenylyl cyclase inhibitor SQ 22536 also inhibited relaxation by VIP.4 In conclusion, our data showed that SNP- and SIN-1-induced relaxation was mediated by sGC. Of sGC inhibitors, methylene blue and LY83583 were not adequate for the examination of NO donor-induced feline LES smooth muscle relaxation. VIP also caused relaxation by the pathway involving NO and cGMP and cAMP.

Notes: 1 The vasoconstrictor response to periarterial nerve electrical stimulation (PNS) and neurotransmission by ATP are discussed and illustrated, using canine isolated and perfused splenic arterial preparations. 2 The conditions for appearance of dominant purinergic constrictor response to PNS are discussed. 3 Modulation of the purinergic vasoconstrictor responses to PNS by several kinds of presynaptic receptor agonists and antagonists is reviewed. 4 Influences of purinergic responses to PNS by guanethidine, reserpine, tetrodotoxin (TTX) or ω-conotoxin GVIA (ωCTX) are also reviewed. 5 Effects of imipramine and removal of the endothelium are discussed. 6 Evidence is presented for selective inhibition of purinergic responses to PNS by an adequate cold storage of the vessel. 7 The roles of ATP released by PNS in isolated canine splenic arteries are proposed.

Notes: 1 The aim of the present study was to investigate the role of several possible neurotransmitters in mediating non-adrenergic, non-cholinergic (NANC) relaxation, and the effects of phosphodiesterase (PDE) III and V inhibitors on adrenergic and NANC relaxation in branch pulmonary artery (PA) of guinea-pig. 2 Under the NANC conditions, electrical field stimulation (EFS, 60 V, 0.2 ms, 20 Hz) induced a tetrodotoxin-sensitive relaxation of the histamine-precontracted PA rings. The nitric oxide (NO) synthase inhibitor NG-nitro-l-arginine methyl ester (l-NAME, 10−4 m) and the guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 10−5 m) partially inhibited the EFS-induced relaxation. The inhibitory effect of l-NAME was reversed completely by l-arginine (10−3 m), but not d-arginine (10−3 m). 3 This NANC relaxation was attenuated by 8-phenyltheophylline (10−5 m), a P1-purinoceptor antagonist. 4 The NANC response was potentiated by 10−6 m zaprinast, a type V PDE inhibitor, but was unaffected by 3 × 10−6 m milrinone, a type III PDE inhibitor. 5 Sodium nitroprusside (SNP) caused a concentration-dependent vasodilator effect which was potentiated by zaprinast, but unaffected by milrinone. Moreover, the effect of combination of zaprinast with milrinone was not significantly different from that observed with zaprinast alone. 6 Isoprenaline produced a concentration-dependent vasodilatation in branch PA of guinea-pig which was potentiated by both zaprinast and milrinone, the efficacy of milrinone being greater than zaprinast. 7 These results suggest that both nitrergic and purinergic pathways are involved in mediating the NANC relaxation in branch PA of guinea-pig. The combination of PDE III or V inhibitors with vasorelaxant drugs may be a hopeful approach for the treatment of pulmonary hypertension.

Notes: 1 The aim of this study was to characterize the histamine receptor type mediating relaxation of the vascular bed of the nasal mucosa from the guinea-pig, and to determine the role of cyclo-oxygenase products and nitric oxide in this relaxant response to histamine. These studies were performed in isolated nasal mucosae examined in vitro to obtain potencies of histamine receptor-type selective agonists in causing vasorelaxation and to determine affinities of histamine receptor antagonists for inhibiting histamine-induced relaxation. 2 After contraction of nasal mucosae with noradrenaline, histamine caused a maximal relaxation response that was 75 ± 6% of the contraction caused by noradrenaline with a mean EC50 value of 4.3 ± 0.5 μm. Neither dimaprit (H2-receptor selective) nor R-α-methylhistamine (H3-receptor selective) caused significant relaxation of nasal mucosae. In contrast, betahistine (H1-receptor selective) caused an 81 ± 7% relaxation of noradrenaline-induced tone with an EC50 value of 15 ± 1 μm. 3 pA2 experiments were performed to obtain KB values of chlorpheniramine (H1-receptor selective) and diphenhydramine (H1-receptor selective) for blocking histamine-stimulated relaxation of nasal mucosae. KB values for chlorpheniramine (0.87 nm) and diphenhydramine (7.4 nm) were consistent with their interaction at the H1-receptor type. Additionally, neither 10 μm cimetidine (H2-receptor selective) nor 1 μm thioperamide (H3-receptor selective) had any effect on the relaxation curve for histamine. 4 In the presence of 10 μm indomethacin (cyclo-oxygenase inhibitor), histamine caused a maximal relaxation response of 73 ± 5% of the noradrenaline-induced tone with an EC50 value of 2.9 ± 0.2 μm, which was not different from control values (EC50 = 5.0 ± 0.4 μm; maximal relaxation = 71 ± 6%). In contrast, 200 μm NG-nitro-l-arginine (nitric oxide synthase inhibitor) completely inhibited histamine-induced relaxation of nasal mucosae. 5 In conclusion, data from the present study suggest only the H1-receptor type mediates relaxation of nasal mucosal blood vessels to histamine, and histamine-induced relaxation of nasal mucosae is entirely dependent on nitric oxide production.

Notes: 1 This study was aimed at evaluating the effect of rutin and harmaline (1-methyl-7-methoxy-3,4-dihydro-β-carboline) on the development of the surgically induced reflux oesophagitis, on gastric secretion, lipid peroxidation, polymorphonucleocytes (PMNs) accumulation, superoxide and hydroxyl radical production in PMNs, cytokine [interleukin-1β (IL-1β), tumour necrosis factor-α (TNF-α)] production in blood and [Ca2+]i mobilization in PMNs. 2 Rutin and harmaline significantly prevented the development of reflux oesophagitis and gastric secretion. Treatments of oesophagitis rats with rutin and harmaline inhibited lipid peroxidation, and myeloperoxidase (MPO) in the oesophagus in comparison with untreated rats. 3 Superoxide anion and hydrogen peroxide production in 1 μm formylmethionylleucylphenylalanine (fMLP)- or 0.1 μg ml−1N-phorbol 12-myristate 13-acetate (PMA)-activated PMNs was inhibited by rutin and harmaline in a dose-dependent fashion. Rutin and harmaline effectively scavenged the hydroxyl radical and hydrogen peroxide. Treatments of oesophagitis rats with rutin and harmaline inhibited IL-1β production in the oesophagus in comparison with untreated rats, but TNF-α production was not affected by rutin and harmaline. The fMLP-induced elevation of [Ca2+]i was inhibited by rutin. 4 The results of this study suggest that rutin and harmaline may have beneficial protective effects against reflux oesophagitis by the inhibition of gastric acid secretion, oxidative stress, inflammatory cytokine production (i.e. IL-1β), and intracellular calcium mobilization in PMNs in rats.

Notes: 1 Although monumental efforts have been made to define the action sites of cough, the importance of neurotransmitter systems in the cough reflex has received limited attention. We studied the roles for four major neurotransmitters [acetylcholine, histamine, serotonin (5-hydroxytryptamine, 5-HT) and dopamine] in the modulation of the cough reflex. 2 Atropine (muscarinic cholinergic blocking agent), pyrilamine maleate (PM, histamine H1 blocker), cimetidine (histamine H2 blocker), 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT, specific 5-HT1A receptor agonist) and SCH-23390 (selective dopamine D1 receptor antagonist) were examined on the cough response to inhaled capsaicin in conscious guinea-pigs. 3 All the drugs significantly decreased the number of capsaicin-induced coughs in a dose-dependent manner. To compare the sensitivity of these drugs on cough response, we calculated the effective doses for 50% inhibition of cough (ED50) when the animals were exposed to 3 × 10−4 m capsaicin. The ED50 values were 0.03 μm kg−1 for atropine, 0.2 μm kg−1 for 8-OH-DPAT, 6.2 μm kg−1 for SCH-23390, 8.5 μm kg−1 for PM and 13.9 μm kg−1 for cimetidine. 4 These findings indicated that all these four neurotransmitters may be involved in the regulation of the cough reflex. Multiple changes of these neurotransmitters in disorders of the central nervous system might synergically affect the cough reflex.

Notes: 1 We have investigated the actions of the α1D-adrenoceptor selective antagonist BMY 7378 in comparison with yohimbine at α1- and α2-adrenoceptors. 2 In rat aorta (α1D-adrenoceptor), BMY 7378 (pA2 of 8.67) was about 100 times more potent than yohimbine (pA2 of 6.62) at antagonizing the contractile response to noradrenaline. 3 In human saphenous vein (α2C-adrenoceptor), BMY 7378 (pA2 of 6.48) was approximately 10 times less potent than yohimbine (pA2 of 7.56) at antagonizing the contractile response to noradrenaline. 4 In prostatic portions of rat vas deferens, BMY 7378 (10 μm) did not significantly affect the concentration-dependent inhibition of single pulse nerve stimulation-evoked contractions by xylazine (an action at prejunctional α2D-adrenoceptors). 5 In ligand-binding studies, BMY 7378 showed 10-fold selectivity for α2C-adrenoceptors (pKi of 6.54) over other α2-adrenoceptors. 6 It is concluded that BMY 7378, in addition to α1D-adrenoceptor selectivity in terms of α1-adrenoceptors, shows selectivity for α2C-adrenoceptors in terms of α2-adrenoceptors.

Notes: 1 To investigate anti-inflammatory activity of organic germanium, we measured the effect of germanium-concentrated yeast on arachidonic acid release, prostaglandin E2 (PGE2) production, histamine release, and intracellular H2O2 or hydroperoxide generation in RBL 2H3 cells, and carrageenan-induced paw oedema in rats. 2 Germanium-concentrated yeast dose-dependently inhibited carrageenan-induced paw oedema, suggesting that germanium-concentrated yeast has anti-inflammatory activity in acute inflammation. 3 Germanium-concentrated yeast significantly inhibited melittin-induced arachidonic acid release and PGE2 production in RBL 2H3 cells. 4 Germanium-concentrated yeast did not affect melittin-induced histamine release and silica-induced intracellular H2O2 or hydroperoxide generation in RBL 2H3 cells. 5 These results suggest that anti-inflammatory activity of germanium-concentrated yeast appears partly to be related to the inhibition of arachidonic acid release and PGE2 production in RBL 2H3 cells.

Notes: 1 The pressor action of noradrenaline and its blockade by selective α1-adrenoceptor antagonists in the pithed mouse were evaluated. 2 Chloroethylclonidine (α1B/D-adrenoceptor alkylating agent) or BMY 7378 (α1D-adrenoceptor antagonist), both at 1 mg kg−1, did not block the increase in blood pressure induced by noradrenaline. 3 5-Methylurapidil (α1A-adrenoceptor antagonist), at 0.1 mg kg−1, displaced the dose–response curve approximately six-fold to the right. 4 The results support the idea that the pithed mouse vasculature express α1A-adrenoceptors and suggest that it is a good model to study the roles of α1-adrenoceptors in gene knockout or overexpression.

Notes: 1 The aim of this paper was to determine the different signalling cascades involved in contraction of the rat urinary bladder detrusor muscle mediated via muscarinic acetylcholine receptors (muscarinic AChR). Contractile responses, phosphoinositides (IPs) accumulation, nitric oxide synthase (NOS) activity and cyclic GMP (cGMP) production were measured to determine the reactions associated with the effect of cholinergic agonist carbachol. The specific muscarinic AChR subtype antagonists and different inhibitors of the enzymatic pathways involved in muscarinic receptor-dependent activation of NOS and cGMP were tested. 2 Carbachol stimulation of M3 and M4 muscarinic AChR increased contractility, IPs accumulation, NOS activity and cGMP production. All of these effects were selectively blunted by 4-DAMP and tropicamide, M3 and M4 antagonists respectively. 3 The inhibitors of phospholipase C (PLC), calcium/calmodulin (CaM), neuronal NOS (nNOS) and soluble guanylate cyclase, but not of protein kinase C and endothelial NOS (eNOS), inhibited the carbachol action on detrusor contractility. These inhibitors also attenuated the muscarinic receptor-dependent increase in cGMP and activation of NOS. 4 In addition, sodium nitroprusside and 8-bromo-cGMP, induced negative relaxant effect. 5 The results obtained suggest that carbachol activation of M3 and M4 muscarinic AChRs, exerts a contractile effect on rat detrusor that is accompanied by an increased production of cGMP and nNOS activity. The mechanism appears to occur secondarily to stimulation of IPs turnover via PLC activation. This in turn, triggers cascade reactions involving CaM, leading to activation of nNOS and soluble guanylate cyclase. They, in turn, exert a modulator inhibitory cGMP-mediated mechanism limiting the effect of muscarinic AChR stimulation of the bladder.

Notes: 1 The objective was to investigate a possible contribution of a nerve-derived hyperpolarizing factor to the differences between non-adrenergic non-cholinergic (NANC) nerve-mediated relaxations in different states of active tone in the rat gastric fundus. 2 NANC relaxations induced by electrical field stimulation (ES: 0.1, 0.5 and 1 Hz; 25 V; 1 ms; 10 s) in 40% contracted strips (S40) were greater when compared with those in 80% contracted strips (S80). 3 ES-induced relaxations were effectively attenuated by Nω-nitro-l-arginine (l-NNA; 100 μm) in S40 and S80. Percentage reduction of the responses obtained in the presence of l-NNA in S40 group was less than that of S80. 4 In S40 group, nifedipine (0.5–1 μm) and verapamil (0.5–1 μm) inhibited the responses to 0.1 and 0.5 Hz. Nifedipine (1 μm) and verapamil (0.5 μm) caused no change in the responses to ES in S80. 5 In S40, when l-NNA (100 μm) and nifedipine or verapamil, either in 1 μm concentration, were administered together, the inhibition on the electrical relaxations were more than that of each drug alone. 6 In conclusion, NANC nerve-mediated relaxations are increased when studied in an active state of 40%, and a factor, sensitive to nifedipine seems to be responsible for this distinction.

Notes: 1 Experiments were carried out to characterize the possible adrenergic properties of the 5-HT1A antagonists WAY 100635 and MM-77 using the mouse isolated vasa deferentia preparation. 2 When vasa deferentia were preincubated for 10 min in the presence of MM-77 (10−8–10−6 m) or WAY100635 (10−8–7 × 10−7 m), a concentration-dependent inhibition of the contractile response to submaximal electrical field stimulation (10 Hz, 50 V, 50 ms) was observed with pIC50 values of 7.05 ± 0.01 and 6.85 ± 0.1 respectively. 3 MM-77 (10−8–10−6 m) antagonized the contractile responses of the vasa deferentia to phenylephrine (PE) (10−6–10−3 m) in a concentration-dependent manner. Schild plots of these data were linear and yielded a mean ρA2 value of 6.81 ± 0.084. The mean slope was 1.42 ± 0.22. 4 WAY100635 (10−8–10−6 m) antagonized the contractile responses of the vasa deferentia to PE (10−6–10−3 m) in a concentration-dependent manner. Schild plots of these data were linear and yielded a mean ρA2 value of 7.05 ± 0.08. The mean slope was 0.97 ± 0.1. 5 The results suggest that while WAY100635 acts as a competitive antagonist at α1-adrenoceptors, MM-77 displays non-competitive antagonist characteristics at this receptor subtype. 6 These results may have important implications for the use of these compounds as 5-HT1A receptor antagonists in in vivo studies.

Notes: 1 The aim of the present study was to examine the modulator influence of muscarinic M2 receptors on responses of rat urinary bladder detrusor muscle evoked by endogenous stimuli, i.e. by stimulation of the bladder innervation. 2 Responses were evoked by electrical field stimulation (EFS; 2–20 Hz, 0.8 ms, 60 V) of isolated strip preparations mounted in organ baths. The tension of the muscle strips was recorded digitally. EFS was performed by applying stimulation with either a short duration (5 s) or a longer duration (to reach peak response; approximately 20 s). 3 Effects of muscarinic receptor antagonists (muscarinic M1/M3 receptor selective: 4-diphenylacetoxy-N-methylpiperidine methobromide (4-DAMP); muscarinic M2 receptor selective: methoctramine), a β-adrenergic antagonist (propranolol) and an adenosine receptor antagonist (8-p-sulfophenyltheophylline) were assessed on contractile activity and on poststimulatory relaxations. 4 Low concentrations of methoctramine (10−8 m) reduced or tended to reduce the EFS-induced contraction, e.g. at 2 Hz by 12% while methoctramine at 10−7 m had no significant effect. In addition, in the presence of 4-DAMP (10−9 m), which tended to inhibit contractions at all frequencies (2–20 Hz; −17 to −25%), methoctramine at 10−8 and 10−7 m induced a further reduction of the contractile responses (−5 to −10%; 2–20 Hz). 5 The β-adrenergic receptor antagonist propranolol (10−6 m) and the adenosine receptor antagonist 8-p-sulfophenyltheophylline (10−6 m) both increased contractile responses by 9–21% (2–10 Hz, long duration; P 〈 0.05–0.001) as a consequence of antagonizing relaxatory stimuli. Neither antagonist affected the contractile responses to EFS with the short duration stimulation. Poststimulatory relaxations were reduced by 30–60% (P 〈 0.05) by propranolol and by 40–60% (P 〈 0.001) by 8-p-sulfophenyltheophylline, but for 8-p-sulfophenyltheophylline only after stimulation with the short duration. 6 In the presence of methoctramine (10−7 m), the 8-p-sulfophenyltheophylline-induced increases of the contractile response to long duration EFS were significantly enhanced at 10 Hz (+12 ± 4%; P 〈 0.05), whereas no such enhancement of the propranolol inhibitory effect occurred in the presence of methoctramine. However, poststimulatory β-adrenoceptor-evoked relaxations after short duration EFS were increased by about 35% in the presence of methoctramine, but not those after long duration. 7 Thus, muscarinic M2 receptor activation inhibits adenosine receptor- and β-adrenoceptor-evoked relaxations of the rat detrusor muscle. The inhibition occurs via a transient postjunctional mechanism that mainly affects responses with a short latency.

Notes: 1 To clarify the effects of doxapram on the baroreflex, we recorded carotid sinus nerve (CSN) activity in isolated and perfused carotid artery bifurcations of rabbits. 2 The CSN activity due to chemoreceptor stimulation was blocked by resection of the nerve branches from the carotid body. After the resection, the CSN activity was correlated to increase of carotid sinus (CS) pressure. 3 Administration of doxapram reduced the CSN activity originating from baroreceptors. The effect of doxapram on baroreceptors was dose dependent and reversible. 4 It is unlikely that doxapram altered CS wall mechanics because CS pressure did not change in the presence of the drug. 5 We conclude that doxapram acts on the cardiovascular system in part by inhibiting the negative feedback loop that originates in CS baroreceptors.

Notes: 1 Cardiac glycosides have been used for centuries as therapeutic agents for the treatment of heart diaseases. In patients with heart failure, digoxin and the other glycosides exert their positive inotropic effect by inhibiting Na+–K+-ATPase, thereby increasing intracellular sodium, which, in turn, inhibits the Na+/Ca2+ exchanger and increases intracellular calcium levels. As the therapeutic index of digitalis is narrow, arrhythmias are common problems in clinical practice. The mechanisms and mediators of these arrhythmias, however, are not completely understood. 2 The involvement of the sympathetic and parasympathetic nervous system in digitalis cardiac toxicity is reviewed. 3 Receptors, channels, exchange systems or other cellular components involved in digitalis-induced cardiotoxicity are also reviewed. 4 Possible mediators of digitalis-induced cardiac toxicity are discussed. 5 Management of digitalis toxicity in patients is summarized. 6 The determination of the possible mediators of digitalis-induced cardiac toxicity will enhance our knowledge and lead to the development of new therapeutic strategies to treat these lethal arrhythmias.

Notes: 1 Microinjection of peptide YY (PYY) (0.23–2.3 nmol) into the posterior hypothalamic nucleus (PHN) of conscious rats evokes a dose-dependent pressor response and a bradycardia. 2 The increase in mean arterial pressure evoked by 2.3 nmol of PYY was not blocked by intravenous pretreatment with: (i) the nicotinic ganglionic receptor antagonist pentolinium (PENT, 10 mg kg−1) alone, or in combination with the muscarinic receptor antagonist methylatropine (MeATR, 1 mg kg−1); (ii) the α1-adrenoceptor antagonist prazosin (PRAZ, 0.2 mg kg−1); (iii) the V1-vasopressin receptor antagonist [d(CH2)5Tyr(Me)]AVP (AVPX, 20 μg kg−1); (iv) the combination of AVPX, PENT and MeATR; (v) the combination of PRAZ, AVPX, PENT, MeATR, and the α2-adrenoceptor antagonist yohimbine (0.3 mg kg−1); or (vi) the angiotensin II type 1 receptor antagonist ZD 7155 (1 mg kg−1). 3 Adrenal demedullation inhibited the PYY-evoked responses of drug-naïve rats, and rats pretreated with the combination of PENT, MeATR and AVPX. 4 Transection of the splanchnic nerve innervating the adrenal medullae attenuated the bradycardia, as did ZD 7155, but not the PYY-evoked pressor response. 5 Systemic pretreatment of rats with the neuropeptide Y1 receptor antagonist BIBP 3226 (1 mg kg−1) blocked the PYY-evoked cardiovascular changes, but not those evoked by microinjection of carbachol (5.5 nmol) into the PHN. 6 These results suggest that the cardiovascular changes evoked from the PHN by PYY requires the presence of the adrenal medullae, which are stimulated by: (i) a hormone to release an NPY-like substance that evokes the pressor response, and (ii) the splanchnic nerve to evoke the release of a substance that results in the bradycardia.

Notes: 1 We examined whether extremely low frequency electromagnetic fields (ELF-EMF) affect the basal level of cardiovascular parameters and influence of drugs acting on the sympathetic nervous system. 2 Male rats were exposed to sham control and EMF (60 Hz, 20 G) for 1 (MF-1) or 5 days (MF-5). We evaluated the alterations of blood pressure (BP), pulse pressure (PP), heart rate (HR), and the PR interval, QRS interval and QT interval on the electrocardiogram and dysrhythmic ratio in basal level and dysrhythmia induced by β-adrenoceptor agonists. 3 In terms of the basal levels, there were no statistically significant differences among control, MF-1 and MF-5 in PR interval, QRS interval, mean BP, HR and PP. However, the QT interval, representing ventricular repolarization, was significantly reduced by MF-1 (P 〈 0.05). 4 (−)-Dobutamine (β1-adrenoceptor-selective agonist)-induced tachycardia was significantly suppressed by ELF-EMF exposure in MF-1 for the increase in HR (ΔHR), the decrease in QRS interval (ΔQRS) and the decrease in QT (ΔQT) interval. Adrenaline (nonselective β-receptor agonist)-induced dysrhythmia was also significantly suppressed by ELF-EMF in MF-1 for the number of missing beats, the dysrhythmic ratio, and the increase in BP and PP. 5 These results indicated that 1-day exposure to ELF-EMF (60 Hz, 20 G) could suppress the increase in HR by affecting ventricular repolarization and may have a down-regulatory effect on responses of the cardiovascular system induced by sympathetic agonists.

Notes: 1 Cyclic AMP formation has consistently been reported to be desensitized in various tissues including heart of animal models of end-stage renal failure (ESRF). In contrast, reports on desensitization of cAMP formation in ESRF patients remain contradictory. Whether this discrepancy results from a difference between human ESRF and its animal models or from the use of circulating blood cells in the human and various solid tissues in the animal studies, remains unclear. Therefore, we performed three studies with heart and platelets of ESRF patients undergoing haemodialysis or continuous ambulatory peritoneal dialysis and age- and gender-matched controls with normal renal function (n = 11–13 each). 2 In platelets from haemodialysis patients adenylyl cyclase activity in response to receptor-dependent and -independent agonists was reduced by ≈30%, and this could be explained by an alteration at the level of adenylyl cyclase itself. However, no such desensitization was seen in platelets from peritoneal dialysis patients. 3 In hearts from ESRF patients undergoing haemodialysis, β-adrenoceptor density and subtype distribution, cAMP formation in response to the β-adrenoceptor agonist isoprenaline or various receptor-independent stimuli, were very similar to those in control patients but activity of G-protein-coupled receptor kinase was increased by ≈20%. 4 We conclude that conflicting reports on the desensitization of cAMP formation between ESRF patients and ESRF animal models are not explained by the use of solid tissues in animal studies vs. circulating blood cells in patient studies. Rather desensitization of cAMP formation seems to be a less consistent feature of human ESRF than of its animal models.

Notes: 1 We have compared vasoconstriction responses in isolated mesenteric small arteries from mice and rats as elicited by KCl, noradrenaline and the lysosphingolipids sphingosine-1-phosphate (S1P) and sphingosylphosphorylcholine (SPC). 2 Contractile responses to KCl and noradrenaline, but not those of S1P or SPC, were significantly related to vessel diameter in both species. 3 When comparing vessels of similar diameter, contractile responses for KCl and the three agonists were much smaller in mice than in rats, e.g. 8.3 ± 0.4 vs. 14.7 ± 0.7 mn for noradrenaline. 4 Based upon the antagonist rank order of potency of prazosin (pKB 8.80) 〉 B8805-033 (pKB 7.89) 〉 yohimbine (pKB 6.18) ≈ BMY 7378 (pA2 6.03), noradrenaline responses in mice were mediated solely via α1A-adrenoceptors, similar to what repeatedly has been shown in rats. 5 The S1P3 receptor antagonist suramin (100 μm) significantly inhibited responses to S1P and SPC in rats but not in mice, and did not affect noradrenaline responses in either species. 6 We conclude that for any given diameter, mouse mesenteric arteries develop less contraction in response to various stimuli. Noradrenaline acts via α1A-adrenoceptors in both species. Responses to S1P and SPC differ between both species with regard to suramin-sensitivity indicating involvement of different receptor subtypes for lysosphingolipids in both species.

Notes: 1 A fructose (Fru)-enriched diet induces a mild increase in blood pressure associated with hyperglycaemia, hypertriglyceridaemia, and insulin resistance, resembling the human ‘syndrome X’, being an useful model to study hypertension and type 2 diabetes. 2 A sustained elevation of blood pressure is associated with cardiovascular structural modifications such as left ventricular hypertrophy and increased wall thickness:lumen diameter ratio in blood vessels. 3 Prostanoids (PR), metabolites of arachidonic acid through the cyclooxygenase pathway, include vasoactive substances synthesized and released by the vessel walls. 4 The aim of the present study was to analyse, in Fru-treated rats: (i) the morphology of mesenteric vessels and; (ii) the PR production in aorta and mesenteric vessels, in order to assess whether these parameters are related with the haemodynamic alterations observed in this experimental model. 5 Blood pressure, glycaemia and triglyceridaemia, were significantly elevated in both (4 and 22 weeks) Fru-treated groups. Meanwhile body and heart weight as well as insulinaemia were similar between experimental animals and controls. 6 The mesenteric vessels of Fru-treated rats (22 weeks) showed an increased thickness and area of the media when compared with the controls; meanwhile, the lumen diameter was similar in both groups. 7 The Fru treatment for 4 weeks did not modify PR production in aorta, whereas in the mesenteric bed it diminished prostaglandin (PG) E2 release significantly compared with the controls. However, in the group treated for 22 weeks, Fru reduced PGI2 production in the aorta, as assessed by 6-keto-PGF1α measurements. Meanwhile, in the mesenteric bed, the chronic Fru treatment decreased PGE2 release but, rather surprisingly, increased the output of PGI2 when compared with its corresponding controls. 8 In conclusion, the present study shows the existence of an alteration in the morphology of mesenteric vessels in Fru-treated rats, which could be related to an increase in peripheral resistance and the consequent mild hypertension observed in this model. However, a diminished release of vasodilator PRs, such as PGE2 in mesenteric vessels at 4 and 22 weeks and PGI2 in aorta at 22 weeks could further impair the vessel response. The increase in PGI2 observed in the chronic group in mesenteric vessels could be attributed to a compensatory mechanism.

Notes: 1 Electrical field stimulation (EFS) (0.5 ms in train of 2–32 Hz for 300 ms) in smooth muscle of pigeon oesophagus, in the presence of atropine (1 μm) and guanethidine (1 μm), elicited an inhibitory response consisting of a transient hyperpolarization (inhibitory junction potential, IJP) associated with muscle relaxation. 2 Sodium nitroprusside (SNP, 100 μm) induced hyperpolarization correlated to mechanical relaxation. 3 The nitric oxide (NO) synthase inhibitor Nω-nitro-l-arginine (from 0.1 to 100 μm) caused a concentration-dependent reduction of electromechanical response to EFS indicating a role for NO in this response. 4 Apamin (1 μm) reduced both IJP and relaxation to EFS but was without effect on the response to SNP indicating a role for purines, which are also blocked by apamin. 5 Adenosine, AMP, ADP and ATP (all from 1 μm to 1 mm) application caused transient hyperpolarization and muscular relaxation with the following order of potency: adenosine 〉 AMP 〉 ADP 〉 ATP. 6 Inhibitory responses evoked by purines are TTX (1 μm) insensitive but they were inhibited by apamin. This indicates that a purine component for the non-adrenergic non-cholinergic (NANC) response exists but the purine receptor site is not located on the neurone. 7 Overall these results suggest that NANC inhibitory response elicited by EFS presents two different components apamin-sensitive, probably purines-mediated and apamin-insensitive probably NO-mediated as apamin only partially block the response to EFS.

Notes: 1 Sibenadet (Viozan®), a dual dopamine D2/β2-adrenoceptor agonist, suppresses histamine-induced tachypnoea in the dog by activating dopamine D2 receptors. We here compare the effects of sibenadet and formoterol, a selective β2-adrenoceptor agonist, on histamine-induced tachypnoea in the rhesus monkey. 2 Anaesthetized, spontaneously breathing, rhesus monkeys were set up for measuring airways resistance, respiratory rate, blood pressure and heart rate. 3 Both sibenadet and formoterol administered by aerosol, induced inhibition of the bronchoconstrictor response to aerosolized methacholine accompanied by tachycardia. Sibenadet, but not formoterol, also reduced blood pressure. 4 Administration of histamine by inhalation induced tachypnoea which was accompanied by bronchoconstriction. Tachypnoea to histamine was suppressed by both sibenadet and formoterol at doses which manifest anti-bronchoconstrictor activity. These effects and the accompanying tachycardia but not the hypotension induced by sibenadet were abolished by pretreatment with propranolol. 5 The dopamine D2 receptor agonist, quinagolide, did not suppress tachypnoea to histamine despite inducing a fall in blood pressure indicating activation of dopamine D2 receptors. 6 Thus, both sibenadet and formoterol suppress histamine-evoked tachypnoea in the rhesus monkey. The effect arises exclusively through activation of β2-adrenoceptors and probably reflects the anti-bronchoconstrictor effects of these agents. The results reveal a fundamental difference in the role of dopamine receptors in the airways of dog and rhesus monkey.

Notes: 1 The present survey is dealing with the interactions between the renin–angiotensin–aldosterone system (RAAS) and the sympathetic nervous system (SNS) in various organs and tissues, with an emphasis on the angiotensin AT-receptors located at the sympathetic nerve endings. 2 Angiotensin II, the main effector of the RAAS is known to stimulate sympathetic nerve traffic and its sequelae in numerous organs and tissues, such as the central nervous system, the adrenal medulla, the sympathetic ganglia and the sympathetic nerve endings. These stimulatory effects are mediated by AT1-receptors and counteracted by AT1-receptor antagonists. 3 Sympatho-inhibition at the level of the sympathetic nerve ending appears to be a class effect of the AT1-receptor blockers, mediated by presynaptic AT1-receptors. With respect to the ratio pre-/postsynaptic AT1-receptor antagonism important quantitative differences between the various compounds were found. 4 Both the pre- and postjunctional receptors at the sympathetic nerve endings belong to the AT1-receptor population. However, the presynaptic receptors belong to the AT1B-subtype, whereas the postjunctional receptors probably belong to a different AT1-receptor subpopulation. 5 Sympatho-inhibition is a class effect of the AT1-receptor antagonists. In conditions in which the SNS plays a pathophysiological role, such as hypertension and congestive heart failure, this property may well be of therapeutic relevance.

Notes: 1 The psychostimulant constituent of khat leaves, S-(−)-cathinone, was examined for vascular activity on the coronary vasculature of guinea-pig-isolated perfused hearts and aortic ring preparations. 2 Cathinone caused coronary vasoconstriction, negative inotropy and negative chronotropy in isolated hearts. The major metabolite of cathinone after its ingestion, 1R.2S-(−)-norephedrine (norephedrine), also caused coronary vasoconstriction comparable with that by cathinone. Norephedrine, however, had no effect on force or rate of cardiac contractions. 3 Cocaine (10 μm) potentiated the coronary vasoconstriction and positive inotropy by noradrenaline indicating inhibition of neuronal uptake. The vasoconstriction and negative inotropy by cathinone, however, were not affected, indicating that its action was not via release of noradrenaline from sympathetic neurones. 4 The α1-adrenoceptor antagonist, prazosin, blocked the vasoconstriction by noradrenaline, but not that produced by cathinone in the presence of cocaine. This indicates that the coronary vasoconstriction by cathinone was not due to an action on α1-adrenoceptors either directly or indirectly through noradrenaline release. 5 Three repeated doses of cathinone displayed the same coronary vasoconstrictor responses, indicating a lack of tachyphylaxis and therefore confirming that the response was unlikely to be due to indirect sympathomimetic activity through release of noradrenaline. 6 In guinea-pig aortic rings, the order of vasoconstrictor activity was: noradrenaline 〉 norephedrine 〉 cathinone, with each causing approximately equivalent maximum responses. The time to reach plateau contractions was shortest for noradrenaline (5.1 ± 0.5 min), then norephedrine (9.3 ± 1.5 min) and cathinone the longest (25.4 ± 3.2 min, 335 μm dose). 7 These results indicate that cathinone has vasoconstrictor activity which is not due to indirect or direct sympathomimetic activity. The precise mechanism for this vasoconstriction remains to be determined. The coronary vasoconstriction may explain the increased incidence of myocardial infarction in khat chewers, which may arise from coronary vasospasm.

Notes: 1 A variety of prostanoids were examined for their ability to alter the periarterial nerve stimulation-induced release of noradrenaline (NA) and neuropeptide Y immunoreactive compounds (NPY-ir) from the perfused mesenteric arterial bed of the rat. 2 Periarterial nerve stimulation (16 Hz) increased the overflow of NA, NPY-ir and perfusion pressure. 3 The prostacyclin (PGI2) analogues, carbaPGI2 and cicaprost both produced a concentration-dependent attenuation of the nerve stimulation-induced increase in NA, NPY-ir overflow and perfusion pressure. 4 The prostaglandin (PG) analogue PGE2 attenuated the evoked increase in NPY-ir overflow as well as a modest decrease in NA. 5 PGE1, sulprostone and iloprost attenuated the nerve stimulation-induced increase in NA overflow but not NPY-ir. 6 Neither PGF2α nor the thromboxane A2 analogue U46619 altered the evoked increase in NA or NPY-ir overflow. 7 The results support the view that sympathetic co-transmitter release can be differentially modulated by paracrine/autocrine mediators at sympathetic neuroeffector junctions.

Notes: 1 Experiments were undertaken to determine if the imidazoline/α2-adrenoceptor agonist, rilmenidine, would produce mydriasis in cats and, if so, to delineate its site of action and determine if this effect is mediated by imidazoline receptors or α2-adrenoceptors. 2 Rilmenidine produced dose-related pupillary dilator responses in pentobarbital anaesthetized cats that were independent of sympathetic innervation to the iris but were dependent upon intact parasympathetic neuronal tone. The ED50 for rilmenidine-induced pupillary dilation was approximately 200 μg kg−1, i.v., and was sustained for at least 1 h. 3 The highly selective α2-adrenoceptor antagonist, RS-79948, administered either before or after rilmenidine, antagonized rilmenidine-induced mydriasis. Neuronally induced reflex inhibition of parasympathetic nerve activity was also inhibited by administration of RS-79948. 4 These results suggest that rilmenidine acts like clonidine to produce pupillary dilation by inhibition of parasympathetic tone to the iris sphincter and that this central nervous system parasympatho-inhibition is mediated by α2-adrenoceptors, rather than imidazoline receptors.

Notes: 1 Increasing evidence indicates the occurrence of functional interconnections between immune and nervous systems, although data available on the mechanisms of this bi-directional cross-talking are frequently incomplete and not always focussed on their relevance for neuroimmune modulation.
2 Primary (bone marrow and thymus) and secondary (spleen and lymph nodes) lymphoid organs are supplied with an autonomic (mainly sympathetic) efferent innervation and with an afferent sensory innervation. Anatomical studies have revealed origin, pattern of distribution and targets of nerve fibre populations supplying lymphoid organs.
3 Classic (catecholamines and acetylcholine) and peptide transmitters of neural and non-neural origin are released in the lymphoid microenvironment and contribute to neuroimmune modulation. Neuropeptide Y, substance P, calcitonin gene-related peptide, and vasoactive intestinal peptide represent the neuropeptides most involved in neuroimmune modulation.
4 Immune cells and immune organs express specific receptors for (neuro)transmitters. These receptors have been shown to respond in vivo and/or in vitro to the neural substances and their manipulation can alter immune responses. Changes in immune function can also influence the distribution of nerves and the expression of neural receptors in lymphoid organs.
5 Data on different populations of nerve fibres supplying immune organs and their role in providing a link between nervous and immune systems are reviewed. Anatomical connections between nervous and immune systems represent the structural support of the complex network of immune responses. A detailed knowledge of interactions between nervous and immune systems may represent an important basis for the development of strategies for treating pathologies in which altered neuroimmune cross-talking may be involved.

Notes: 1 Calcium/calmodulin-dependent protein kinase II (CaMKII) has an important function in mediating insulin release but its role in the development of diabetes-induced cardiovascular complications is not known. 2 We investigated the ability of a chronic administration of KN-93 (5 mg kg−1alt diem for 4 weeks), an inhibitor of CaMKII, to modulate the altered vasoreactivity of the perfused mesenteric bed to common vasoconstrictors and vasodilators in streptozotocin (STZ)-induced diabetes. 3 The vasoconstrictor responses induced by noradrenaline (NE), endothelin-1 (ET-1), and angiotensin II (Ang II), were significantly increased whereas, vasodilator responses to carbachol and histamine were significantly reduced in the perfused mesenteric bed of the STZ-diabetic rats as compared with non-diabetic controls. 4 Inhibition of CaMKII by KN-93 treatment did not affect blood glucose levels but produced a significant normalization of the altered agonist-induced vasoconstrictor and vasodilator responses. KN-93 did not affect agonist-induced responses in control animals. In addition, KN-93 significantly reduced weight loss in diabetic rats. 5 The present data suggest that CaMKII is an essential mediator in the development of diabetic vascular dysfunction and may also play an important role in signalling pathways leading to weight loss during diabetes.

Notes: 1 There is good evidence that β-blockers improve ventricular function, disease progression and survival in patients with left ventricular systolic dysfunction. The aim of this study was to determine the effects of atenolol therapy on the sympathetic nervous system at rest and after ergometric exercise, on left ventricular function and on baseline plasma atrial natriuretic factor (ANF) in ambulatory patients with chronic heart failure (CHF). 2 Twenty-two patients [left ventricular ejection fraction (LVEF) 〈36%; New York Heart Association II–III] were studied before atenolol treatment. Because of cardiac events (new Hospital admission or death) only 13 patients completed 1 year of treatment. Baseline noradrenaline (NE) concentrations were similar in patients and controls while ANF was higher in patients than in controls (328 ± 35 pg ml−1vs. 37 ± 3 pg ml−1; P 〈 0.01). 3 Patients with events showed higher NE (540 ± 87 pg ml−1vs. 303 ± 44 pg ml−1; P 〈 0.01) and ANF (460 ± 70 pg ml−1vs. 291 ± 44 pg ml−1; P 〈 0.03) at rest; and greater NE response to exercise (2.003 ± 525 pg ml−1vs. 694 ± 121 pg ml−1; P 〈 0.005). Atenolol treatment improved LVEF (19.5 ± 1.9%vs. 33 ± 3.9%; P 〈 0.001), increased exercise tolerance (9 ± 3.2 min vs. 17 ± 4.8 min; P 〈 0.001) and decreased plasma ANF (292 ± 42 pg ml−1vs. 133 ± 35 pg ml−1; P 〈 0.01). 4 Reduced basal dihydroxyphenylglycol (DHPG)/NE ratio (3.4 ± 0.46 vs. 4.3 ± 0.35; P 〈 0.01) was observed in patients compared with healthy volunteers. Atenolol increased DHPG plasma levels (1.398 ± 129 pg ml−1vs. 913 ± 86 pg ml−1; P 〈 0.005) but the DHPG/NE ratio during exercise was not modified after treatment, suggesting that re-uptake of released NE is not changed by β-blocker treatment. 5 In conclusion, the fact that atenolol treatment improves ventricular dysfunction and clinical status without changing plasma NE levels in CHF patients, suggests that plasma NE is a poor surrogate measurement for cardiac sympathetic activity in this pathology. In addition, decrease in plasma ANF produced by atenolol treatment may reflect the improvement of ventricular function.

Notes: 1 The aim of the study was to investigate the role of the α1D-adrenoceptor in α1-adrenoceptor-induced contraction of human prostate by means of protection experiments. 2 Responses of human prostate strips to noradrenaline were recorded, along with responses of rat aorta and vas deferens, tissues possessing predominantly α1D- and α1A-adrenoceptors respectively, for comparison. α1-adrenoceptors were then inactivated by incubation with the irreversible antagonist phenoxybenzamine. In some tissues α1A- or α1D-adrenoceptors were ‘protected’ from inactivation by incubation in the presence of the selective α1A- or 1D-adrenoceptor antagonists 5-methylurapidil and BMY 7378 before recording further responses to noradrenaline. 3 Phenoxybenzamine reduced the maximum noradrenaline-induced response and the potency of noradrenaline in all tissues. In rat vas deferens and human prostate, 5-methylurapidil protected α1A-adrenoceptors in a concentration–dependent manner. In rat aorta, 10 nm BMY 7378 almost fully protected α1D-adrenoceptors. However, concentrations of BMY 7378 up to 30-fold higher failed to protect receptors in the human prostate. 4 These results suggest that in human prostate functional α1D-adrenoceptors do not contribute to noradrenaline-induced contractile responses.

Notes: 1 A triple organ bath method allowing the synchronous recording of the motor activity of the circular muscle layer belonging to the oral and anal segments of guinea-pig small intestine adjacent to an electrically stimulated middle segment was developed to study the ascending and descending reflex motor responses. 2 Electrical field stimulation (0.8 ms, 40 V, 5 Hz, 10 s) applied to the middle part of the segments elicited tetrodotoxin (1 μm)-sensitive ascending and descending contractile responses of the nonstimulated parts, oral and anal, respectively. The ascending contraction was more pronounced as compared with the descending contraction. 3 In the presence of phentolamine (5 μm), propranolol (5 μm) and atropine (3 μm) a significant decrease in the amplitude of the ascending contraction was seen and a descending relaxation, instead of a contraction was observed. 4 Met-enkephalin applied at a single concentration (0.1 μm) or cumulatively (0.001–1 μm) inhibited both non-adrenergic non-cholinergic (NANC) descending relaxation and ascending contraction with similar efficacy but different potency, IC50 being 5.9 ± 0.3 and 39.0 ± 4 nm, respectively. Naloxone (0.5 μm) prevented the effects of Met-enkephalin. 5 L-NNA (0.5 mm), an inhibitor of nitric oxide synthesis, increased the ascending contraction and strongly reduced but not abolished the descending relaxation. l-Arginine (0.5 mm) restored the motor responses to the initial level in l-NNA-pretreated preparations, d-Arginine (0.5 nm) had no effects. 6 Met-enkephalin (0.1 μm) depressed the l-NNA-dependent increase of the ascending contraction and failed to change the l-NNA-resistant part of the descending relaxation. 7 Met-enkephalin did not alter spontaneous NANC mechanical activity. SNP (1 or 10 μm), an exogenous donor of nitric oxide, caused a concentration-dependent relaxation. The effects of SNP persisted in Met-enkephalin (0.1 μm)-pretreated preparations. 8 NANC reflex ascending contraction and descending relaxation were synchronously induced by a local nerve stimulation indicating a functional coactivation of NANC orally projected excitatory and anally directed inhibitory pathways. Acting prejunctionally, Met-enkephalin provided a negative controlling mechanism inhibiting both ascending and descending, mainly nitric oxide mediated, reflex responses. A higher sensitivity of the descending relaxation to Met-enkephalin was observed suggesting an essential role of opioid(s) in reducing the efficacy of descending motor activity.

Notes: 1 The present study was designed to investigate the secretion of catecholamines (CA) evoked by stimulation of cholinergic receptors and membrane depolarization from the isolated perfused adrenal gland of spontaneously hypertensive rats (SHR) and normotensive Wistar–Kyoto rats (WKYR) at adult age. 2 The wet weight of adrenal gland in SHR was greater than that in WKYR. The CA releasing responses evoked by acetylcholine (5.32 × 10−3 m), and high potassium (5.6 × 10−2 m), a membrane depolarizer, were significantly lower in WKYR than in SHR. 3 The secretory responses of CA evoked by DMPP (10−4 m for 2 min), a selective agonist of neuronal nicotinic receptors, and McN-A-343 (10−4 m for 2 min), a selective agonist of neuronal muscarinic receptors, were also significantly lower in WKYR than in SHR. 4 The CA release evoked by Bay-K-8644 (10−5 m), a dihydropyridine-sensitive Ca2+ channel activator, and cyclopiazonic acid (10−5 m), a selective inhibitor of Ca2+-ATPase in the endoplasmic reticulum, were also significantly greater in SHR than WKYR. 5 Taken together, these experimental results demonstrate that the CA secretion evoked by stimulation of cholinergic (nicotinic and muscarinic) receptors as well as membrane depolarization is enhanced more greatly in the perfused adrenal glands of SHR than in those of WKYR. It is suggested that the augmented CA release in SHR compared with WKYR was involved in essential hypertensive pathogenesis.

Notes: 1 The contractile capacity of smooth muscle cells depends on the cytoskeletal framework of the cell. The aim of this study was to determine the functional importance of both the actin and the tubulin components of the cytoskeleton in contractile responses of the bovine isolated iris sphincter muscle. 2 In each preparation, two contractions to the muscarinic agonist carbachol were obtained. The maximum responses of the first contractions were taken as 100%. The second contractions to carbachol were elicited in the presence of either cytochalasin B (50 and 5 μm), an inhibitor of the actin cytoskeleton, or colchicine (100 μm), an inhibitor of the tubulin cytoskeleton (30 min incubation). 3 Cytochalasin B, at a concentration of 50 μm, significantly decreased the contractions induced by carbachol, with the maximum response reduced to 21.8 ± 6.6% (n = 12) of the initial maximum. The maximal contractions to carbachol in the presence of colchicine reached 96.2 ± 7.9% (n = 9) of the initial contraction, which was not significantly different from control second responses to carbachol with neither drug present, which reached 113.3 ± 7.6% (n = 7). 4 The effect of cytochalasin B was dose-dependent, since at a lower concentration of 5 μm, the drug decreased the maximum contraction to carbachol to 60.3 ± 8.8% (n = 6). The effect of cytochalasin B was at least partially reversible, since after the use of the higher concentration of 50 μm, contractions to carbachol increased to 62.3 ± 15.5% (n = 4) of the maximal response, after 1 h repeated washing of the preparations. 5 Cytochalasin D, at a concentration of 50 μm, completely abolished the contractions induced by carbachol (n = 4). 6 These findings suggest that in bovine iris sphincter muscle, contractions to carbachol are highly dependent, from a functional point of view, on actin polymerization, and not, to any important degree, on the polymerization of tubulin.

Notes: 1 The parasympathetic nervous system is responsible for maintaining normal bladder function, contracting the bladder smooth muscle (detrusor) and relaxing the bladder outlet during micturition. 2 Contraction of the bladder involves direct contraction via M3 receptors and an indirect ‘re-contraction’ via M2-receptors whereby a reduction in adenylate cyclase activity reverses the relaxation induced by β-adrenoceptor stimulation. 3 Muscarinic receptors are also located on the epithelial lining of the bladder (urothelium) where they induce the release of a diffusible factor responsible for inhibiting contraction of the underlying detrusor smooth muscle. The factor remains unidentified but is not nitric oxide, a cyclooxygenase product or adenosine triphosphate. 4 Finally, muscarinic receptors are also located prejunctionally in the bladder on cholinergic and adrenergic nerve terminals, where M1-receptors facilitate transmitter release and M2 or M4-receptors inhibit transmitter release. 5 In pathological states, changes may occur in these receptor systems resulting in bladder dysfunction. Muscarinic receptor antagonists are the main therapeutic agents available for treatment of the overactive bladder, but whether their therapeutic effect involves actions at all three locations (detrusor, prejunctional, urothelial) has yet to be established.

Notes: 1 In this study, we have investigated the vasodilator response to acetylcholine under diabetes conditions in isolated renal arteries of rabbits. We have also examined the contribution of endothelium-derived nitric oxide (EDNO) and endothelium-derived hyperpolarizing factor (EDHF) to the endothelium-dependent relaxation caused by acetylcholine in the renal arteries of alloxan-induced diabetic rabbits. 2 Acetylcholine (10−10−10−4 m) produced cumulative concentration–response curve in the renal arteries of both control and diabetic rabbits. The EC50 values and maximal responses to acetylcholine were not significantly different relative to diabetic conditions. In order to isolate the EDHF component of acetylcholine-induced vasodilator response, l-nitro-methyl arginine ester (l-NAME, 10−4 m) and indomethacin (10−6 m) were added to the Krebs' solution throughout the experiment. Under these conditions, acetylcholine induced vasodilatation in the isolated renal arteries from both control and diabetic rabbits. The vasodilator response to acetylcholine was not affected under diabetic conditions. 3 Sodium nitroprusside (SNP)-induced relaxation was increased in the diabetic rabbits compared with the control animals. 4 Tetrabutyl ammonium (TBA, 0.5 mm) produced a significant reduction in acetylcholine-induced vasodilatation in both preparations from control and diabetic animals, consistent with involvement of K+ channels in mediating this response. Glibenclamide (1 μm) attenuated acetylcholine-induced vasodilatation in preparations from control animals only, while iberiotoxin (0.05 μm) significantly reduced the vasodilator response to acetylcholine in preparations from both control and diabetic animals. 5 The role of EDNO in mediating acetylcholine-induced vasodilatation was examined. The vascular preparations were incubated with 20 mm K+-Krebs' solution to inhibit the EDHF contribution to acetylcholine-induced vasodilatation. Under this condition, acetylcholine induced a vasodilator response in both preparations from control and diabetic rats. Pretreatment with l-NAME (10−4 m) attenuated acetylcholine-induced vasodilatation in both preparations, indicating an nitric oxide-mediated vasodilator response. 6 Our results indicated that acetylcholine-induced vasodilatation in the isolated renal arteries of alloxan-induced diabetic rabbits was not affected under diabetic conditions. Acetylcholine-induced vasodilatation is mediated by two vasodilator components; namely, EDHF and EDNO. The contribution of EDHF and EDNO to acetylcholine-induced vasodilatation was not affected under diabetic conditions and there was no indication of endothelial dysfunction associated with diabetes. EDHF component was found to act mainly through high conductance Ca2+-activated K+ channels under normal and diabetic conditions, while the adenosine triphosphate-dependent K+ channels were involved in mediating acetylcholine vasodilator response in the control preparations only.

Notes: Summary 1 It was shown recently that stimulation of cardiac muscarinic M2-receptors revealed an enhanced negative inotropic response in isolated rat left atria after exposure to hypochlorite-induced oxidative stress. This phenomenon was not observed after stimulation of the cardiac A1-receptor, which like the M2-receptor is coupled to Gi-proteins. Since even the contractile response to M3-receptor stimulation was not amplified in the rat portal vein, we hypothesized a M2-receptor specificity of this hypochlorite-induced enhancement. 2 The present study was performed in order to investigate whether the sympathoinhibitory response to presynaptically located M2-receptor stimulation would also be modified after exposure to hypochlorite in the rat tail artery. We applied electrical field stimulation (EFS) in order to mimic sympathetic neurotransmission. 3 EFS increased the vascular tone frequency-dependently (0.3–4 Hz). EFS-induced vasoconstriction could be attenuated by acetylcholine (30 nm−1 μm) in a concentration-dependent manner. Hypochlorite (10 and 100 μm) did not affect the sympathoinhibitory effect of acetylcholine (100 nm). 4 In conclusion, in contrast to cardiac M2-receptors, hypochlorite did not amplify the sympathoinhibitory effects of presynaptic M2-receptors. The different responsiveness between neuronal and cardiac M2-receptors to hypochlorite may be explained by the different G-protein subunits involved in the activation of the underlying signalling cascade.

Notes: 1 Our aim was to study the role of nitric oxide (NO) and arachidonic acid pathways in the α1-adrenoceptor-mediated vasoconstriction in mesenteric resistance arteries from 3–4 and 22 to 23-month-old Sprague-Dawley rats. 2 The expression of NO synthase (NOS), cyclooxygenase (COX) isoforms, soluble guanylate cyclase, superoxide dismutase and the NAD(P)H oxidase subunits p22phox and p47phox were determined. 3 The NG-nitro-l-arginine methyl ester, a non-selective NOS inhibitor, shifted to the left but indomethacin and NS 398, non-selective and selective COX-2 inhibitors, shifted to the right the concentration-response curve for the vasoconstriction by phenylephrine in both age groups. 4 Ageing up-regulated endothelial NOS and p22phox expression but did not modify COX, soluble guanylate cyclase, superoxide dismutase and p47phox expression. 5 These data suggest that the observed enhancement of eNOS protein expression could constitute a compensatory mechanism to counter-regulate a chronic loss of NO possibly through increased superoxide anion production from NAD(P)H oxidase induced by age.

Notes: 1 The effect of WAY 405 ((R)-N-(2-methyl-(4-indolyl-1-piperazinyl)ethyl)-N-(2-pyridinyl) cyclohexane carboxamide), a putative 5-HT1A receptor antagonist, on cardiovascular function was studied. 2 In anaesthetized rats, the i.v. injection of WAY 405 did not significantly modify basal heart rate nor blood pressure at doses of 1, 3, 10 and 30 μg kg−1; while the antagonist dose dependently antagonized the 5-HT1A receptor agonist, 8-OH-DPAT (8-hydroxy-2-(di-n-propylamino)tetralin)-induced hypotension and bradycardia. 3 WAY 405 antagonized noradrenaline-induced contraction in isolated arteries, with pKB values of 6.6 ± 0.1, 6.5 ± 0.1 and 6.5 ± 0.1, for rat tail artery (α1A-adrenoceptors), rabbit aorta (α1B-adrenoceptors), and rat aorta (α1D-adrenoceptors) respectively. 4 The results show that in the control of blood pressure the new compound, WAY 405, behaves as a silent 5-HT1A receptor antagonist in the anaesthetized rat, also having low affinity for vascular α1-adrenoceptors.

Notes: 1 Chronic cold exposure of rats (7 days in a cold room at 4 °C) attenuated the sympathetic nerve stimulation (NS)-induced overflow of noradrenaline (NE) (measured by high-performance liquid chromatography, coupled to electrochemical detection) appearing in the perfusate/superfusate of the perfused mesenteric arterial bed as well as the increase in the perfusion pressure. 2 The same type of cold exposure resulted in an increase in tyrosine hydroxylase (TH) gene expression measured in the superior cervical ganglion and NE content measured in the mesenteric artery obtained from cold-exposed rats. 3 Addition of sodium nitroprusside, a nitric oxide (NO) donor, to the buffer perfusing the mesenteric arterial bed obtained from rats maintained at room temperature also resulted in an attenuation of the NS-induced overflow of NE and increase in perfusion pressure. 4  N c-nitro-l-arginine methyl ester (l-NAME), an NO synthase inhibitor, placed in the drinking water prevented the attenuation of the pre- and post-junctional responses to NS of the mesenteric arterial bed obtained from cold-exposed rats. 5  l-NAME treatment also increased the cold-induced elevation of blood pressure seen in whole animals. 6 The present results are consistent with the idea that cold exposure leads to a concomitant increase in sympathetic nerve activity and production of NO. We hypothesize that the increase in production and release of NO results in a decrease in the biologically active form of NE despite increased synthesis and release of the catecholamine. 7 It is concluded that the above-mentioned interactions serve as a protective mechanism offsetting the increased release and action of NE from sympathetic nerves and thus preventing the development of hypertension.

Notes: 1 G-protein-coupled receptor signalling, including transactivation of receptor tyrosine kinases (RTKs), has been implicated in vascular pathology. However, the role of specific RTKs in the development of diabetes-induced cardiovascular complications is not known. 2 We investigated the ability of a chronic administration of genistein, a broad-spectrum inhibitor of tyrosine kinases (TKs), AG1478, a specific inhibitor of epidermal growth factor receptor (EGFR) TK activity, and AG825, a specific inhibitor of Erb2, to modulate the altered vasoreactivity of isolated carotid artery ring segments to common vasoconstrictors and vasodilators in streptozotocin (STZ)-induced diabetes. 3 In diabetic carotid artery, the vasoconstrictor responses induced by noradrenaline (NE), endothelin-1 (ET-1), and angiotensin II (Ang II), were significantly increased whereas vasodilator responses to carbachol and histamine were significantly reduced. Inhibition of TKs, EGFR or Erb2 pathway did not affect the body weight or agonist-induced vasoconstrictor and vasodilator responses in the non-diabetic control animals. However, inhibition of TKs by genistein, EGFR TK by AG1478 or Erb2 by AG825 treatment produced a significant normalization of the altered agonist-induced vasoconstrictor responses without affecting blood glucose levels. Treatment with diadzein, an inactive analogue of genistein, did not affect the vasoconstrictor and vasodilator responses in the diabetic animals. 4 Treatment with genistein, AG1478 or AG825 resulted in a significant improvement in diabetes-induced impairment in endothelium-dependent relaxation to carbachol and histamine. 5 These data suggest that activation of TK-mediated pathways, including EGFR TK signalling and Erb2 pathway, are involved in the development of diabetic vascular dysfunction in the carotid artery.

Notes: 1 We have investigated the actions of the calcium entry blockers nifedipine, R-verapamil and S-verapamil in rat aorta, colon and vas deferens. 2 In aorta and colon, these agents produced concentration-dependent relaxations of KCl (80 mm)-induced contractions. In both tissues, the order of potency was nifedipine 〉 S-verapamil 〉 R-verapamil. However, nifedipine showed selectivity for aorta (potency ratio, colon/aorta: 4.36), S-verapamil showed no selectivity (0.62), but R-verapamil showed selectivity for colon (0.19). 3 In prostatic portions of rat vas deferens, nifedipine (10 μm) abolished the contraction to a single electrical stimulus, but R- and S-verapamil were without effect. In epididymal portions of rat vas deferens, R- and S-verapamil inhibited α1-adrenoceptor-mediated contractions to a single electrical stimulus at concentrations of 10 μm and above. 4 In conclusion, R-verapamil may prove useful as an intestinal selective calcium entry blocker in the treatment of intestinal disease with a hypermotility component, e.g. irritable bowel syndrome.

Notes: 1 The present study was carried out to pharmacologically identify the β-adrenoceptor subtype that mediates isoprenaline-elicited relaxation in the isolated guinea-pig tracheal smooth muscle, to answer the question whether it is β1- or β2-subtype? 2 Isoprenaline as well as salbutamol, a well-known β2-selective adrenoceptor agonist, produced a concentration-dependent relaxation with a pD2 value of 8.12 vs. 7.54 for salbutamol. 3 Isoprenaline-elicited relaxation was not affected by β1-selective antagonists, atenolol and CGP-20,712A, within the concentration ranges supposed to antagonize β1-subtype: atenolol, ≤10−6 m; CGP-20,712A, ≤10−8 m. 4 By contrast, the concentration–response curves for isoprenaline as well as salbutamol were shifted rightwards in a competitive fashion by atenolol at the concentrations ≥3 × 10−6 m. However, pA2 values of atenolol against isoprenaline (5.86) and salbutamol (5.71) were consistent with the value corresponding to β2- but not to β1-subtype (around 7.00), and these values were not significantly different from each other. 5 Competitive antagonism of the relaxations to isoprenaline and salbutamol were also obtained with β2-selective antagonists, butoxamine and ICI-118,551. Against isoprenaline and salbutamol, the pA2 values of butoxamine (6.51 vs. 6.81) and ICI-118,551 (8.83 vs. 8.90) were substantially identical. Thus the primary mediation of β2-receptor in the relaxations was strongly supported. 6 The present findings provide evidence that the β-adrenoceptor which mediates isoprenaline-elicited relaxation of guinea-pig tracheal smooth muscle is essentially β2- but not β1-subtype. The present study also indicates the importance of using multiple receptor antagonists with different pA2 values to pharmacologically identify the responsible receptor subtype in smooth muscle mechanical responses.

Notes: 1 The role of histamine in heat-induced cardiovascular changes is uncertain. The purpose of this study was to examine effects of histamine H-1- and H-2-antagonism on heart rate, mean arterial blood pressure (MAP), localized body temperature changes, survival times, and lethal body temperatures that occur during the exposure of anaesthetized rats to 35 GHz radio frequency radiation (RFR). 2 Forty-eight ketamine-anaesthetized Sprague–Dawley rats were exposed, in several different treatment groups (n = 8 in each), to 35 GHz RFR at a level that resulted in significant body heating and subsequent death. During irradiation, a continuous increase in heart rate and a biphasic response in blood pressure (initial increase followed by a decrease) were observed in all groups of animals. 3 An H-1-antagonist, diphenhydramine (1 mg kg−1 body wt) and an H-2-antagonist, cimetidine (5 mg kg−1), administered after sustained RFR exposure, failed to reverse the RFR-induced hypotension. High doses of the drugs (5 and 10 mg kg−1, respectively) also did not alter the response. Post-RFR survival time was significantly decreased in the high-dose drug-treated group, compared with vehicle-treated (0.9% NaCl, 50% ethanol and 50% D5W) controls. 4 In experiments in which the two drugs were administered prior to RFR exposure, MAP in animals receiving high-dose antihistamines was significantly depressed compared with that of vehicle-treated animals during the first 35 min of RFR exposure. Antihistamine pretreatment, however, did not alter the total RFR exposure time required for death to occur. 5 In summary, pharmacological blockade of H-1 and H-2 receptors is not beneficial in anaesthetized rats made hypotensive by RFR exposure. This indicates that activation of H-1 and H-2 receptors by histamine does not occur to any significant extent and does not mediate the hypotensive response developed in this model of hyperthermia.

Notes: 1 In the present investigation we examined the regulation of calmodulin (CaM)- and protein kinase C (PKC)-dependent pathways by cytosolic Ca2+ in the contraction of cat lower oesophageal sphincter (LES). 2 Force developed in response to increasing doses of acetylcholine (ACh) was directly related to the increase of the [Ca2+]i measured by fura-2. Thapsigargin, which depletes Ca2+ stores, reduced the contraction and the [Ca2+]i. In addition, contraction in response to maximal ACh was reduced by the CaM inhibitor CGS9343B but not by the PKC inhibitor chelerythrine. The contraction in response to submaximal ACh was reduced by chelerythrine but not by CGS9343B. 3 In permeabilized cells, the contraction in response to low Ca2+ (0.54 μm) was also reduced by CGS9343B. 4 The response to high Ca2+ (1.0 μm) was reduced by CGS9343B. ACh also inhibited PKC activation induced by diacylglycerol, which activation is inhibited by the N-myristoylated peptide inhibitor derived from pseudosubstrate sequences of PKCαβγ (myr-PKC-αβγ), but not of myr-PKC-α. 5 These data are consistent with the view that activated CaM-dependent pathways inhibit PKC-dependent pathways, this switch mechanism might be regulated by Ca2+ in the LES.

Notes: 1 Approximately 45% of patients with diabetes mellitus have gastrointestinal complications such as diarrhoea and constipation, but the underlying aetiology is unclear. The present study investigates alterations in spontaneous motility of the colon that may be, in part, responsible for these symptoms using an established animal model of diabetes.2 Rats were rendered diabetic by a single intraperitoneal injection of streptozotocin and age-matched controls were injected with citrate buffer. Rats were sacrificed after 8-weeks and proximal colonic circular muscle tissue mounted in organ baths.3 Spontaneous activity was observed in both control and diabetic tissues, but this activity was almost doubled in colonic tissue taken from diabetic rats. It was hypothesized that this increase was due to a deficit in inhibitory control of the colon in the diabetic state.4 Possible alterations in nitrergic and vasoactive intestinal polypeptide (VIP)ergic control were investigated using a range of pharmacological tools.5 Sodium nitroprusside, VIP and antioxidants (reduced glutathione, ascorbate and α-tocopherol) inhibited the spontaneous activity, but the level of inhibition observed was not different in diabetic tissue compared with control.6 Arginine, [d-p-Cl-Phe6, Leu17]-VIP and α-chymotrypsin had no effect on spontaneous activity in either sets of tissue.7 N-nitro-l-arginine produced a small, but significant, increase in the level of spontaneous activity, but the degree of increase was not different between control and diabetic tissues.8 Western blots demonstrated that there was no inducible-nitric oxide synthase (iNOS) in control or diabetic tissues and that the levels of endothelial-NOS (eNOS) and neuronal-NOS (nNOS) detected were not statistically significantly different. The [3H]-citrulline assay established that the functionality of the NOS isoforms present were unaltered in the diabetic state.9 This study demonstrates that there is a marked alteration in motility in the colon taken from diabetic animals. However, the change in motility is unlikely to be due to a change in inhibitory control mechanisms and may be due to an increased excitability.

Notes: 1 Pig nasal mucosal strips were incubated with α-adrenoceptor antagonists followed by α2-adrenoceptor agonist concentration–response curves. 2 Contractions elicited by the α2-adrenoceptor agonists BHT-920 (pD2 = 6.16 ± 0.07), UK 14,304 (pD2 = 6.89 ± 0.13) and PGE-6201204 (pD2 = 7.12 ± 0.21) were blocked by the α2-adrenoceptor antagonist yohimbine (0.1 μm). In contrast, the α1-adrenoceptor antagonist prazosin (0.03 μm) had no effect on the BHT-920-, UK 14,304- and PGE-6201204-induced contractions, but blocked the contractile response to the α1-adrenoceptor agonist phenylephrine (pD2 = 5.38 ± 0.04) and the mixed α1- and α2-adrenoceptor agonist oxymetazoline (pD2 = 6.30 ± 0.22). 3 The α2-adrenoceptor antagonist yohimbine (0.01–0.1 μm, pA2 = 8.04), α2B/C-adrenoceptor antagonist ARC 239 (10 μm, pKb = 6.33 ± 0.21), α2A/C-adrenoceptor antagonist WB 4101 (0.3 μm, pKb = 8.01 ± 0.24), α2A-adrenoceptor antagonists BRL44408 (0.1 μm, pKb = 6.82 ± 0.34) and RX 821002 (0.1 μm, pKb = 8.31 ± 0.35), α2C-adrenoceptor antagonists spiroxatrine (1 μm, pKb = 7.32 ± 0.32), rauwolscine (0.1 μm, pKb = 8.16 ± 0.14) and HV 723 (0.3 μm, pKb = 7.68 ± 0.14) inhibited BHT-920-induced contractions in pig nasal mucosa. 4 The present antagonist potencies showed correlations with binding affinity estimates (pKi) obtained for these antagonists at the human recombinant α2A- and α2C-adrenoceptors (r = 0.78 and 0.83, respectively) and with binding affinity estimates (pKd) obtained in pig native α2A- and α2C-monoreceptor assays (r = 0.85 and 0.78, respectively). No correlation was observed for the α2B-subtype. 5 In conclusion, contractile responses to phenylephrine, BHT-920, UK 14,304, PGE-6201204 and oxymetazoline indicate that α1- and α2-adrenoceptors are present and mediate vasoconstriction in pig nasal mucosa. Furthermore, correlation analysis comparing antagonist potency in pig nasal mucosa with affinities for human recombinant α2-adrenoceptors and native pig α2-adrenoceptors suggest that α2A- and α2C-adrenoceptor subtypes constrict pig nasal mucosa vasculature.

Notes: 1 The relationship between the effects of endogenous nitric oxide (NO) and prostanoids on the noradrenaline (NA)-induced contractions and the mechanisms involved were investigated in the rat perfused mesenteric bed, using NG-nitro-l-arginine methyl ester (l-NAME), a NO synthase inhibitor and sodium nitroprusside (SNP), a NO donor.2 The constrictor responses to NA were reduced to 50% by the cyclooxygenase inhibitor 10 μm indomethacin as well as by 1 μm SNP. When indomethacin and SNP were perfused simultaneously the contractions were further reduced.3 The NA-induced contractions were increased by the addition of 400 μml-NAME and the addition of either indomethacin or SNP abolished such increases. The simultaneous perfusion of both agents further reduced the contractions.4 Removal of the endothelium increased NA-induced contractions to a similar extent as l-NAME and this increase was abolished by indomethacin as well as by SNP.5 The perfusion of 10 μm NA augmented the release of prostaglandin (PG) F2α by the mesenteric bed without modifications in any other prostanoid. In the presence of l-NAME, this effect was further increased. However, SNP abolished the NA-induced stimulation of PGF2α release.6 In de-endothelialized preparations NA also stimulated PGF2α production as observed in intact preparations. This effect was more marked in the presence of l-NAME; in contrast, SNP abolished the stimulation.7 In conclusion, the present results suggest an opposite action between NO and PGF2α on the NA-induced contractions in the rat mesenteric bed.

Notes: 1 The present study was carried out to characterize the effect of adenosine on calcium dynamics in the rat portal vein. Isolated portal vein of male albino rats was used as the experimental model as it exhibits autorhythmicity. Adenosine and its analogues 2-CAD, N6-CHA and NECA were used to characterize the type of adenosine receptor involved and 2-CAD was used along with adenosine throughout the other part of study to characterize the effect of adenosine on Ca2+ dynamics.2 Adenosine and its analogues were found to inhibit the spontaneous contractions of rat portal vein in a concentration-related manner. The order of potency was NECA 〉 2-CAD 〉 N6-CHA 〉 adenosine. Incubation of the tissue with CGS∼15943A, an adenosine receptor antagonist, had a per se enhancing effect on autorhythmicity. Adenosine and 2-CAD failed to reverse the contractile response produced by hypertonic KCl (80 or 30 mm). Whereas adenosine and 2-CAD effectively relaxed the tissues contracted with phenylephrine (10−5 m).3 Preincubation of the tissue with 2-CAD (10−4, 10−5 or 10−6 m) for 5 min raised the threshold concentration of CaCl2 to evoke contractile response and also significantly increased the mean EC50 values of CaCl2. Nifedipine was found to be more potent than 2-CAD on Ca2+ channels.4 The results of the present study suggest that the endogenous adenosine plays a significant role in producing vascular relaxation through the participation of A2 receptor subtype. This effect may be due to its inhibitory effect on release of Ca2+ from the intracellular stores. Further to this effect, 2-CAD had a major inhibitory effect on voltage-operated Ca2+ channels compared with receptor-operated Ca2+ channels.5 It can be concluded that adenosine through its A2 receptor produces vasorelaxant effect by interfering with the release of Ca2+ from the intracellular stores coupled with influx of Ca2+ from the extracellular sources.

Notes: 1 The prolonged infusion of 1,3-dipropyl-8-sulfophenylxanthine (DPSPX), a non-selective antagonist of adenosine receptors, induces hypertension, an increase in plasma renin activity and morphological cardiovascular changes. 2 The aim of this work was to evaluate the effects of losartan, a selective AT1 receptor antagonist, and atenolol, a β-adrenoceptor antagonist, on DPSPX-induced hypertension. 3 Male Wistar rats (250–300 g, n = 4–6) were treated for 1 or 4 weeks with: saline i.p.; DPSPX (90 μg kg−1 h−1) i.p.; losartan (15 mg kg−1 day−1) p.o.; atenolol (25 mg kg−1 day−1) p.o.; DPSPX (90 μg kg−1 h−1) i.p. + losartan (15 mg kg−1 day−1) p.o.; DPSPX (90 μg kg−1 h−1) i.p. + atenolol (25 mg kg−1 day−1) p.o. Blood pressure was measured by the ‘tail-cuff’ method in conscious animals. Fragments of the mesenteric and tail arteries were processed for morphological study and the mean diameter of the vascular smooth muscle cells was determined. 4 DPSPX increased blood pressure. Losartan and atenolol prevented this rise but had no effect on blood pressure of control rats. DPSPX-treated groups showed hypertrophy of the vascular smooth muscle cells and proliferation of subintimal cells. Losartan but not atenolol prevented these changes. Losartan had no effect on the vascular morphology of control rats, while treatment with atenolol for 4 weeks induced hypertrophy of the vascular smooth muscle cells. 5 Both losartan and atenolol counteract the development of DPSPX-induced hypertension but only losartan prevents the alterations in vascular morphology.

Notes: 1 The effects of intraperitoneal (i.p.) lipopolysaccharide on vascular reactivity to noradrenaline in rat aorta under different conditions of passive tension, as well as on mortality in normotensive and hypertensive rats, were studied. 2 Concentration–response curves to noradrenaline were obtained in aorta rings, at two levels of passive tension: 3 and 0.5 g, from control and lipopolysaccharide-treated Wistar rats. Contractile responses were expressed as percentage of the maximal response to noradrenaline obtained in the beginning of the experiment at a resting tension of 2 g. The maxima were significantly larger (P 〈 0.05) at 3 g than at 0.5 g in both groups of rats: 117.8 vs. 62.3%, respectively, for control animals; 85.8 vs. 32.5%, respectively, for lipopolysaccharide-treated rats. 3 The 24-h mortality after the i.p. administration of lipopolysaccharide was lower in spontaneously hypertensive rats (1/12; 8%), when compared with control Wistar–Kyoto rats (5/11; 45%). However, mortality was higher in Wistar–Kyoto made hypertensive by 8-day administration of corticosterone (6/6; 100%). 4 We conclude that a differential sensitivity to noradrenaline of aortic smooth muscle at two different levels of passive tension is still present in lipopolysaccharide-treated animals. Chronic hypertension in SHR rats is associated with resistance to the lethal effects of lipopolysaccharide, whereas abrupt-onset hypertension induced by corticosterone leads to an increased mortality. 5 These results are compatible with the myofibrillary hypothesis, which explains vascular hyper-reactivity in chronic arterial hypertension, by postulating that a more favourable relative position (and/or proportion) for actin and myosin occurs, whereas in states of vascular hypo-reactivity, such as vasodilatory shock, the opposite phenomenon may exist.

Notes: 1 The present study aimed to evaluate the role of κ-opioid receptors at two peripheral sites, the vas deferens and the proximal colon, in κ-opioid receptor knockout mice. We investigated the role of the κ-opioid receptor in the vas deferens twitch response and in the colonic ‘off-contraction’, a rebound contractile response which follows the inhibitory response to low frequencies stimulation (10, 20, 30 Hz) and which has been suggested to ‘locally’ reproduce the contractile component of the peristaltic reflex. 2 Transmural stimulation of the vas deferens at lower frequencies (10 Hz, 10 V, 1 ms pulse trains lasting 0.5 s) evoked a contractile response that was significantly higher in the preparations from knockout mice because of lack of κ-opioid receptors than in wild type mice. A selective κ-opioid receptor agonist, U-50,488H, induced a dose-dependent inhibition of the electrically stimulated contraction in vas deferens. The percentages of reduction of the twitch response were significantly lower in knockout mice than in wild type mice after treatment with U-50,488H. The reduction of twitch response caused by U-50,488H was not reversed by administration of nor-binaltorphimine (nor-BNI) (5 × 10−6 m), a selective κ-opioid receptor antagonist, in preparations from both knockout mice and wild type mice. U-50,488H has no effect on postsynaptic adrenergic receptors, as its administration did not affect the direct contractile response to noradrenaline. 3 Transmural stimulation (5 Hz, 20 V, 2 ms pulse trains lasting 30 s) induced inhibition of spontaneous activity of colonic strips during the period of stimulation, followed by an ‘off-contraction’ after the cessation of stimulation. The statistical evaluation of the ‘off-contraction’ responses between the two strains showed no significant difference. The off-contraction, measured in specimens from knockout mice, was inhibited concentration-dependently by U-50,488H (P 〈 0.01) and significantly less than from wild type mice. 4 The effect of U-50,488H was not reversed by administration of nor-BNI (5 × 10−6 m), either in preparations from knockout mice or from wild type mice. 5 Our data may suggest that κ-opioid receptors are involved in some peripheral responses to the nerve stimulation, as indicated by the effect of U-50,488H, a selective κ-opioid receptor agonist. However, the involvement of κ-opioid receptor was also present, although less apparent, in κ -opioid receptor knockout mice, suggesting either that this drug acts not only on κ-opioid receptors but also on other receptor sites, such as κ-like receptors. An alternative interpretation can be related to a sodium channel blocking action of U-50,488H, which could explain the inhibitory effects of twitch response still present but less evident in knockout strain and the lack of effect of the antagonist nor-BNI.

Notes: 1 The effects of neuropeptide Y (NPY) upon the isolated vasculature are reviewed. 2 The vasconstrictor responses to periarterial nerve stimulation (PNS) and neurotransmission by noradrenaline (NA) and ATP are discussed and illustrated using canine isolated perfused splenic artery. 3 Modulation of the vascular responses to PNS by NPY via pre- and post-junctional NPY Y2 and Y1 receptors is discussed. 4 Evidence is presented for different α1-adrenoceptor subtypes mediating vasoconstriction to exogenous and endogenously released NA and their different locations in the neurovascular junction and extrajunctional regions. 5 Activation of NPY Y1-receptors potentiates sympathetic nerve activated α1-adrenoceptor vasoconstriction. The proposal that the postjunctional α1B adrenoceptor may be linked to the NPY Y1-receptor and is responsible for co-operation between sympathetic and NPYergic interactions in the vasculature is discussed.

Notes: Summary 1 GABAB1 receptor subunit knockout mice were generated and the effects of the GABAB receptor agonist, baclofen, were evaluated within the peripheral nervous system (PNS) of wildtype (+/+), heterozygote (+/–) and knockout (–/–) animals. For this purpose, neuronally-mediated responses were evoked in both the isolated ileum and urinary bladder, using selective electrical field stimulation (EFS). 2 In ileum resected from 4–8-week-old-mice, low frequencies of EFS (0.5 Hz) evoked irregular muscle contractions which were prevented by atropine 1 μM and reduced by baclofen (33.4 ± 5.6%, 100 μm). The latter effect was antagonized by the GABAB receptor antagonist CGP54626 0.2 μm. Baclofen 100 μm did not affect contractions of similar amplitude induced by carbachol, indicating that the ability of baclofen to inhibit cholinergic function in mouse ileum may be due to an action at prejunctional GABAB receptors. 3 To avoid the development of grand mal seizure by GABAB1 (–/–) mice, a behaviour observed when the mice were greater than 3 weeks old, it was necessary to study the effects of this knockout in 1–3-week-old-animals. However, at this age, EFS at 0.5 Hz did not evoke robust muscle contractions. Consequently we used EFS at 5 Hz, which did evoke cholinergically mediated contractions, found to be of similar amplitude in (+/+) and (+/–) mice, of both 1–3 weeks and 4–8 weeks of age. At this frequency of EFS, baclofen reduced the amplitude of the evoked contractions [n=6 (+/+) and n=5 (+/–), IC50 19.2 ± 4.8 μm) and this effect was greatly reduced in the presence of CGP54626 0.2 μm. 4 In urinary bladder from 1–3-week-old-mice, using higher frequencies of EFS to evoke clear, nerve-mediated contractions (10 Hz), baclofen 10–300 μm concentration-dependently inhibited contractions in (+/+) mice (IC50 9.6 ± 3.8 μm). This effect was inhibited by CGP54626 (0.2 μm, 46.2 ± 13.6% inhibition, 300 μm baclofen n=7) a concentration which, by itself, had no effect on the EFS-evoked contractions. 5 The effects of baclofen in both ileum and urinary bladder were absent in the GABAB1 receptor subunit (–/–) mice; however, responses to EFS were unaffected in (–/–) when compared to the (+/+) mice. 6 Our data suggest that, as in the central nervous system (CNS), the GABAB1 receptor subunit is an essential requirement for GABAB receptor function in the enteric and PNS. As such, these data do not provide a structural explanation for the existence of putative subtypes of GABAB receptor, suggested by studies such as those in which different rank-orders of GABAB agonist affinity have been reported in different tissues.

Notes: 1 Type 2 diabetes is associated with diverse oral pathologies in which salivary flow reduction is one of the causes of these oral abnormalities. Scarce literature exists regarding noradrenergic transmission and adrenergic-induced salivary flow in submaxillary and parotid glands of type 2 diabetic rats. 2 We studied noradrenergic transmission as well as the secretory response to α1- and β-adrenoceptor stimulation in the parotid and submaxillary glands of type 2 diabetic rats. 3 Diabetic rats exhibited diminished neuronal uptake, release and endogenous content of noradrenaline (NE) in both salivary glands. Further, NE synthesis was also diminished accompanied by decreased tyrosine hydroxylase activity. Salivary flow responses to α1-(methoxamine) and β-(isoprenaline) adrenoceptor stimulation were reduced in the submaxillary as well as the parotid glands of diabetic rats. 4 Our results suggest that the reduction of noradrenergic transmission in the salivary glands of type 2 diabetic rats is in part responsible for the diminished salivary flow evoked by α1- and β-adrenergic stimulation. Reduced noradrenergic activity may contribute to the pathophysiology of oral abnormalities in diabetic patients.

Notes: 1 We investigated the effects of exogenously applied steroids and endogenously released cortisol on catecholamine (CA) secretion induced by cholinergic agonists in perfused guinea-pig adrenal glands. 2 Acetylcholine (ACh) and electrical stimulation induced CA secretion, which was reversibly inhibited by cortisol. Adrenocorticotropic hormone (ACTH) increased the concentration of cortisol in the perfusion effluent and partly inhibited the secretory response to ACh. 3 Cortisol or aldosterone dose-dependently inhibited secretory responses to nicotine and muscarine. These inhibitory effects were not antagonized by mifepristone and spironolactone, respective cortisol and aldosterone receptor blockers. 4 Dexamethasone, cortisone, corticosterone, 11-deoxycortisol, 11-deoxycorticosterone, prednisolone and cholesterol inhibited nicotine-evoked CA secretion. The secretory response to muscarine was inhibited by these compounds except for dexamethasone and prednisolone. 5 Dexamethasone, cortisol and aldosterone had no effect on CA secretion induced by high KCl. 6 These results suggest that steroids affect nicotinic and muscarinic ACh receptor-mediated responses through distinct mechanisms, and that cortisol released from the adrenal cortex inhibits CA secretion from the adrenal medulla.

Notes: 1 The aim of this study was to characterize the adenosine receptor mediating vasodilation in the microvasculature of the hamster cheek pouch in vivo. A range of adenosine agonists was used including N6-cyclopentyladenosine (CPA) (A1 agonist), 5′-N-ethylcarboxamidoadenosine (NECA) (non-selective), 2-chloroadenosine (2CADO) (non-selective), 2-p-(2-carboxyethyl)-phenethylamino-5′-N-ethylcarboxamidoadenosine (CGS 21680) (A2A agonist), N6-(3-iodobenzyl)-adenosine-5′-N-methyluronamide (IBMECA) (A3 agonist) and adenosine, as well as the adenosine antagonists 8-sulphophenyltheophylline (8-SPT) (A1/A2 antagonist), 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) (A1 antagonist) and 4-(2-[7-amino-2-(2-furyl)[1,2,4]-triazolo[2,3-a][1,3,5]triazin-5-ylamino]ethyl)phenol (ZM 241385) (A2A antagonist). 2 All the adenosine analogues used induced vasodilation at concentrations between 10 nm and 1 μm, and the potency order was NECA 〉 CGS 21680 〉 2CADO 〉 CPA=IBMECA 〉〉 adenosine, indicating an action at A2A receptors. 8-SPT (50 μm) antagonized vasodilator responses to NECA with an apparent pKB of 5.4, consistent with an action at A1 or A2 receptors and confirming that A3 receptors are not involved in this response. 3 DPCPX (10 nm) had no effect on vasodilation evoked by NECA, suggesting that this response was not mediated via A1 receptors, while ZM 241385 (10 nm) antagonized dilator responses to NECA with an apparent pKB of 8.9 consistent with an action via A2A receptors. 4 Overall these results suggest that adenosine A2A receptors mediate vasodilation in the hamster cheek pouch in vivo.

Notes: 1 The hypothesis that the non-adrenergic, non-cholinergic excitatory (NANC-e) innervation is involved in the induction of asthma and that antagonists of NANC-e neurotransmitter could reduce bronchoconstriction during asthma was tested. 2 The first objective was to identify the neurotransmitter(s) of NANC-e innervation from a group of selected putative neurotransmitters. The second objective was to use the antagonist of the identified neurotransmitter(s) to determine its effectiveness against bronchoconstriction to ovalbumin (OVA) in sensitized guinea-pigs. 3 Neurotransmitter identification was performed using the ‘tracheal pouch’, a surgical preparation established for demonstrating NANC innervation, in anaesthetized guinea-pig airways. A segment of trachea was cannulated and clamped at one end and the other end was connected to a pressure transducer. The stump of the trachea was connected to a ventilator to keep the blood gas values within the normal range. The vagus nerve and the sympathetic nerves were isolated bilaterally and cut. The left carotid artery was cannulated to monitor blood pressure and for sampling blood for blood gas analysis. The jugular vein was cannulated for administration of test agents. 4 Both NANC-e and NANC-i (inhibitory) control responses of airways were obtained by bilateral vagal stimulation after complete autonomic blockade with atropine, propranolol and prazosin. The relaxation of the tracheal pouch was indicative of the NANC-i response and the increase in insufflation pressure of the ventilated peripheral airways was due to NANC-e stimulation. 5 The involvement of the putative neurotransmitters such as neurokinin-A (NK-A), histamine, serotonin and endothelin (ET) was investigated by using the respective antagonists, MEN-10376, pyrilamine maleate, cyproheptadine hydrochloride, and two ET receptor antagonists (BQ-123 and IRL-1038), respectively. The antagonists were administered at the dose rate of 4 mg kg−1 i.v. which was determined from preliminary studies by testing against the respective agonists. 6 MEN-10376 (neurokinin-2 receptor antagonist) significantly inhibited the insufflation pressure (peripheral airway pressure) increase caused by NANC-e stimulation. MEN-10376 also inhibited the fall in blood pressure caused by bilateral vagal stimulation. The 5-HT antagonist, cyproheptadine, significantly enhanced the NANC-e response. 7 After identifying the NANC-e neurotransmitter as NK-A, the effectiveness of its antagonist, MEN-10376, was evaluated for its ability to attenuate the increase in insufflation pressure (bronchoconstriction) induced in guinea-pigs sensitized by OVA. Guinea-pigs were sensitized to OVA (200 mg i.p.) and 10 days later prepared for the determination of tracheal pouch and insufflation responses to 100 μg of OVA administered i.v. (challenge dose). This caused an increase in insufflation pressure in the presence of adrenergic and cholinergic blockade, which was significantly attenuated by MEN-10376. 8 These studies indicated that neurokinin-2 receptors were involved in the vagally mediated efferent neurotransmission of NANC-e and that NANC-e plays a role in allergen-induced bronchoconstriction.

Notes: 1 The effect of WAY100635 (N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl) cyclohexanecarboxamide trihydrochloride), a 5-HT1A receptor antagonist, on cardiovascular function was studied. 2 The i.v. injection of WAY100635 dose-dependently decreased blood pressure in anaesthetized rats; while in pithed rats WAY100635 (1 mg  kg−1) displaced the phenylephrine pressor effect. 3 WAY100635 antagonized phenylephrine-induced contraction in rabbit and rat aorta (pA2 of 6.88 and 7.93 and Schild slopes of −0.83 and −1.21, respectively); while in rat caudal artery pKB was 7.45 and the Schild slope of −0.56, suggesting a complex interaction in this vessel. 4 The results show that WAY100635 induced hypotension in the anaesthetized rat and suggest that this effect could be partially explained by antagonism of vascular α1-adrenoceptors.

Notes: 1 Purinergic transmission from sympathetic nerves in the guinea-pig vas deferens was monitored using intracellular recording techniques. Stimulation of the hypogastric nerve with trains of 15 pulses at 1 Hz evoked excitatory junction potentials (EJPs) which increased in amplitude from the first pulse and reached a maximum after 6–8 pulses. 2 Caffeine (3 and 10 mm), depolarized cells by 5–10 mV and increased the amplitude of the first few EJPs in each train but reduced the maximum amplitude of EJPs late in the train. 3 The adenosine receptor antagonist 8-p-sulphophenyl-theophylline (8-SPT; 30 μm) had no effect on either the resting membrane potential or the EJP amplitude; however, at 100 μm it reduced the amplitude of all EJPs by 5–10%. 4 Adenosine (10 and 30 μm) reduced the amplitude of EJPs in a concentration-dependent manner. The inhibitory effect of adenosine on EJP amplitude was prevented by pretreatment with either caffeine (3 mm) or 8-SPT (30 μm). 5 Ryanodine (30 μm) did not alter EJP amplitude and did not inhibit the enhancement of the first EJP by caffeine (3 mm). Incubation of the tissue with the cell permeable calcium chelator 1-2-bis(o-aminophenoxy)ethane-N,N-N′,N′-tetraacetic acid (BAPT-AM) resulted in a depression of EJP amplitude and a longer time to reach maximum amplitude. In cells that had been exposed to BAPT-AM, caffeine 3 mm still increased amplitude of EJP early in the train. 6 The phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine (IBMX; 500 μm), hyperpolarized cells and increased the amplitude of EJP throughout the train of stimulation. In the presence of IBMX, caffeine 3 mm still depolarized the cells and enhanced the EJP early in the train of stimulation. 7 The findings in this study confirm that caffeine and 8-SPT are effective inhibitors of the actions of adenosine. However, caffeine has an additional action to enhance EJP early during a train of stimulation, which cannot be attributed to blockade of adenosine receptors, but which may be related to inhibition of phosphodiesterase.

Notes: 1 The β3-adrenoceptor agonist ZD 7114, like the non-selective β-adrenoceptor agonist isoprenaline, but unlike the β1-adrenoceptor agonist dobutamine and the β2-adrenoceptor agonist salbutamol, produced an increment on mouse embryonic fibroblast proliferation. The half-maximal stimulation of cell growth occurred at substantially lower concentrations with the β3-adrenoceptor agonist (EC50: 5.5 × 10−8 m) than with isoprenaline (EC50: 1.25 × 10−6 m). 2 The selective β3-adrenoceptor antagonist SR 5923 OA prevented the β3-stimulated fibroblast proliferation. Conversely, practolol and butoxamine did not prevent fibroblast growth. 3 Additionally, a decrease of cAMP was obtained in fibroblasts cells upon stimulation with isoprenaline and ZD 7114. 4 The expression of β-adrenoreceptors on fibroblast cells was also studied by radioligand binding. The Ki values in the presence of β1- and β2-adrenoceptor antagonist was two-fold higher than the Ki values for β3 adrenoceptor antagonist indicating the presence of A3-receptor subtype. 5 Inhibitors of different intracellular coupling pathways including phospholipase C (U 73122), protein kinase C (staurosporine), calcium/calmodulin (trifluoroperazine) and calcium channel (verapamil), prevented the stimulatory actions of the selective β3-adrenoceptor agonist ZD 7114. 6 The presence of β3-adrenoceptors on embryonic mouse fibroblast cells may play a role in the modulation of cell growth and biologic activity. The mechanism by which ZD 7114 triggers cell proliferation and function, involves the activation of phospholipase C, PKC, calcium/calmodulin and the influx of calcium.

Notes: 1 Cytokines may parallel or regulate the beneficial effects of β-adrenoceptor antagonist treatment observed in chronic heart failure (CHF) patients. Therefore, this study was performed in order to investigate alterations of cytokine levels in β-blocker-treated patients suffering from CHF. 2 We investigated plasma cytokine levels in eight healthy controls and 12 CHF patients. The patients were treated with standard medication (CHFstd) or with standard medication and additional β1-blocker metoprolol (CHFmet). Interleukin-(IL)-1α, IL-1β, IL-1 receptor antagonist (IL-1ra), IL-2, IL-6, IL-8, IL-10, tumor necrosis factor-α (TNF), soluble TNF receptor type 1 (sTNF-R1), sTNF-R2, and sCD14 were measured by ELISA. 3 IL-1α and IL-1β were not detectable in any of the tested groups. IL-2, TNF, or sCD14 were not altered as compared with healthy control subjects. CHFstd patients expressed enhanced IL-1ra, IL-6, IL-8, IL-10, sTNF-R1 and sTNF-R2. In CHFmet patients IL-1ra, IL-6 and IL-8 remained at the same level. In contrast, sTNF-R1 levels were significantly reduced, although not to control, whereas the sTNF-R2 and IL-10 were reduced to control levels. 4 The cAMP levels of mononuclear cells – recalculated for the patients included in this study from previous work [Werner et al. (2001). Basic Res. Cardiol., 96, 290]– correlated inversely with the sTNF-R2 data (Pearson, r=−0.46; P=0.041; Spearman, r=−0.64, P=0.002). 5 The present data indicate an interaction of the neurohumoral and the cytokine system in CHF patients at the cAMP level. Thus, measurement and correlation of sTNF-R2 and cAMP may provide a tool useful during investigation of β-blocker therapy.

Notes: 1 The effects of BIIE 0246, a novel and non-peptide neuropeptide Y (NPY) Y2 receptor antagonist on sympathetic vasoconstriction of the canine splenic artery were investigated. 2 The vasoconstrictor response to periarterial electrical nerve stimulation was described to be a double peaked vasoconstriction consisting of an initial transient, dominantly P2X purinoceptor-mediated constriction followed by a prolonged, mainly α1 adrenoceptor-induced response. 3 BIIE 0246 at a concentration of 0.1–1 μm dose-dependently potentiated double peaked constrictions at low frequencies (1 and 4 Hz), whereas at high frequency (10 Hz), it failed to affect these responses. BIIE 0246 (1 μm) also enhanced double peaked responses even in the presence of rauwolscine (0.1 μm). NPY (13–36) (1–100 nm), a selective Y2 receptor agonist reduced these two peaked responses in a dose-related manner. The vasoconstriction to noradrenaline (0.1–10 nmol) or adenosine triphosphate (0.01–1 μmol) was not significantly influenced by either 1 μm BIIE 0246 or 100 nm NPY (13–36). Exposure of tissues to 1 μm BIIE 0246 almost completely prevented the suppression of double peaked constrictions by NPY (13–36) (10 nm) or by NPY (10 nm). 4 We conclude that NPY inhibits sympathetic purinergic and adrenergic vasoconstrictions through an activation of prejunctional Y2 receptor subtype in the neurovascular junction of the canine splenic artery.

Notes: Summary 1 The agonistic and antagonistic effects of labetalol, the α1- and β-adrenoceptor antagonist, were studied on β3-adrenoceptors in the guinea-pig gastric fundus. 2 Labetalol caused a concentration-dependent relaxation with a pD2 value of 5.58 ± 0.09 and an intrinsic activity of 0.64 ± 0.06, which was not affected by pretreatment with both the selective β1-adrenoceptor antagonist, (±)-atenolol (100 μM), and the selective β2-adrenoceptor antagonist, (±)-butoxamine (100 μM). 3 However, the non-selective β1-, β2- and β3-adrenoceptor antagonist, (±)-bupranolol (3–30 μM), shifted the concentration–response curve of labetalol to the right (pA2 value=5.97 ± 0.08). 4 In the presence of (±)-atenolol (100 μM) and (±)-butoxamine (100 μM), relaxations to catecholamines [(−)-isoprenaline, (−)-noradrenaline and (−)-adrenaline], to the selective β3-adrenoceptor agonist, BRL37344, and to the non-conventional partial β3-adrenoceptor agonist, (±)-CGP12177A, were weakly antagonized by labetalol (10 μM). 5 These results indicate that labetalol, the arylethanolamine, acts as a partial agonist on β3-adrenoceptors in the guinea-pig gastric fundus.

Notes: 1  The aim of the current study was to investigate the existence of P2Y4 purinergic receptors in the HT-29 human colon cancer cell line. 2  We utilized Western blots and immunocytochemistry for the analysis. 3  Western blotting demonstrated two bands that could not be found after the antibody had been preabsorbed with the control peptide, suggesting that both bands are related to the P2Y4 purinergic receptor. 4  Immunocytochemistry showed immunoreactivity for the P2Y4 purinergic receptor localized in the cytoplasm of the HT-29 cells. 5  This is the first demonstration of the protein expression of P2Y4 purinergic receptors in a human colon cancer cell line.

Notes: 1 The purpose of this study was to examine the effect of inhibition of the formation of cytochrome P450 metabolites of arachidonic acid with 1-aminobenzotriazole (ABT) on the development of hypertension and end-organ damage in spontaneously hypertensive rats (SHR) chronically treated with nitric oxide synthesis inhibitor l-NAME (SHR-l-NAME). 2 Administration of l-NAME in drinking water (80 mg l−1) to SHR for 3 weeks significantly elevated mean arterial blood pressure (MABP) (223 ± 4 mmHg) as compared to SHR controls drinking regular water (165 ± 3 mmHg). The administration of ABT (50 mg kg−1 i.p. alt diem) for 6 days significantly attenuated elevation of blood pressure in SHR-l-NAME (204 ± 4 mmHg). 3 l-NAME-induced increase in urine volume and protein was significantly lower in ABT-treated animals. 4 The impaired vascular responsiveness to noradrenaline and isoprenaline in the perfused mesenteric vascular bed of SHR-l-NAME-treated animals was significantly improved by ABT treatment. 5 Morphological studies of the kidneys and hearts showed that treatment with ABT minimized the extensive arterial fibrinoid necrosis, arterial thrombosis, significant narrowing of arterial lumen with marked arterial hyperplastic arterial changes that were observed in vehicle treated SHR-l-NAME. 6 In isolated perfused hearts, recovery of left ventricular function from 40 min of global ischaemia was significantly better in ABT-treated SHR-l-NAME. 7 These results suggest that in hypertensive individuals with endothelial dysfunction and chronic NO deficiency, inhibitors of 20-HETE synthesis may be able to attenuate development of high blood pressure and end-organ damage.

Notes: 1 The airways of patients with asthma are hyperresponsive to adenosine. The phenomenon can be mimicked in the actively sensitized Brown Norway rat by exposure to allergen or lipopolysaccharide (LPS). We wondered whether combined treatment with allergen and endotoxin would result in additive effects or synergism with respect to increasing the sensitivity of the airways of the Brown Norway rat to adenosine. 2 Animals actively sensitized to ovalbumin and challenged intratracheally with allergen or endotoxin manifested increased bronchoconstrictor responses to adenosine. A combination of ovalbumin and endotoxin also increased the response to adenosine but the effects were at best additive. 3 Changes in the response to adenosine were selective as responses to 5-hydroxytryptamine were unaltered following ovalbumin or LPS either alone or in combination. 4 Thus, endotoxin and allergen acting together could play a role in up-regulating the response of the human asthmatic airway to adenosine. However, our data suggest that the interaction would be additive rather than synergistic.

Notes: 1 We have characterized the α1-adrenoceptor subtypes present in isolated aorta of the α1D-adrenoceptor knockout (KO) mice, by chloroethylclonidine (CEC)-induced alkylation and their protection by selective α1-adrenoceptor antagonists. 2 The α1D-adrenoceptor is involved in the contractile response to noradrenaline in wild type (WT) mouse aorta. 3 In WT mice 5-methylurapidil (5-MU, an α1A-adrenoceptor antagonist) or BMY 7378 (8-[2-[4-(2-methoxyphenyl)-1-piperazinyl] ethyl]-8-azaspiro[4.5] decane-7,9 dione, a selective α1D-adrenoceptor antagonist), protected the receptors from CEC-induced (α1B/D-adrenoceptor) alkylation, the combination of both antagonists resulted in complete protection, while AH11110A (1-[biphenyl-2-yloxy]-4-imino-4-piperidin-1-yl-butan-2-ol, an α1B-adrenoceptor antagonist) did not protect. 4 In aorta of KO mice there was a 19-fold rightward shift in noradrenaline effective concentration (EC50) compared with WT; while 5-MU alone or in combination with AH11110A protected α1-adrenoceptors to the same extent. 5 The data indicate that α1A-adrenoceptors mediate contraction and suggest their role in maintaining homeostasis in the α1D-adrenoceptors KO mice.

Notes: 1 This study evaluated the inhibitory action of apigenin-7-O-β-d-glucuronopyranoside (AGC), apigenin, and omeprazole on reflux oesophagitis and gastritis in rats. AGC was isolated from Clerodendron trichotomum leaves. 2 Oesophagitis and gastritis were induced by surgical procedure and the administration of indomethacin, respectively. The intraduodenal (i.d.) administration of AGC decreased the volume of gastric juice and increased the gastric pH compared with apigenin and omeprazole. The acid output was more inhibited by AGC in a dose-dependent manner than by apigenin and omeprazole. Compared with apigenin and omeprazole, AGC significantly decreased the size of gastric lesions, which were induced by exposure of the gastric mucosa to indomethacin. 3 Malondialdehyde (MDA) content, which is the end product of lipid peroxidation, was increased significantly after the induction of reflux oesophagitis. The MDA content was decreased by AGC (i.d. 3 mg kg−1), but not by either apigenin or omeprazole. This suggests that AGC has an antioxidative effect. In the oesophagitis group, the mucosal levels of glutathione (GSH) were significantly lower than that in the normal group. However, the GSH levels were preserved after administering the AGC, suggesting that AGC possesses scavenging activity. 4 In summary, AGC is more potent than apigenin and omeprazole at inhibiting reflux oesophagitis and gastritis and may therefore be a promising drug for their treatment.

Notes: 1 The great taxonomic and prey base diversity of colubrids (non-front-fanged snakes) suggests that their venoms may represent a ‘literal gold mine’ for scientists eager to find novel pharmacological probes (Mackessy, 2002). 2 While pharmacological characterization is lacking for most of these venoms, this is even more so with regard to activity of colubrid venoms on the mammalian autonomic nervous system. This study characterizes the activity of venom from the colubrid, Boiga dendrophila using in vitro smooth muscle preparations and the anaesthetized rat. 3 In the prostatic segment of the rat vas deferens, cumulative additions of venom (1–150 μg ml−1) induced concentration-dependent inhibition of electrically evoked (0.2 Hz, 0.3 ms, 70–100 V) twitches. The inhibitory effect of venom (100 μg ml−1) was attenuated by 8-phenyltheophylline (8-PT) (20 μm) and 8-cyclopentyl-1, 3-dipropylxanthine (20 μm) but not idazoxan (1 μm), or a combination of ranitidine (0.2 μm) and thioperamide (10 μm). The inhibitory effect of venom (100 μg ml−1) was augmented by dipyridamole (10 μm) but abolished by pretreatment with adenosine deaminase (7.5 units/100 μl) suggesting that it contains components with adenosine A1 receptor activity, most likely adenosine. 4 In isolated segments of guinea-pig ileum, venom (10–100 μg ml−1) caused concentration-dependent contractions which were inhibited by the muscarinic receptor antagonist atropine (0.1 μm) but not by the histamine receptor antagonist mepyramine (0.5 μm). 5 In the anaesthetized rat, venom (5–7.5 mg kg−1, i.v.) caused a hypotensive effect. 6 Our data suggest that the venom contains components with purinergic and muscarinic receptor activity.

Notes: 1 β-Adrenoceptor (AR) ligands have been the mainstay of cardiovascular therapy for decades, with β-AR antagonist being used for hypertension, angina and myocardial infarction and adrenaline in use for cardiopulmonary resuscitation for nearly 100 years. 2 Ischaemia of the heart through coronary artery occlusion causes cell injury and death through necrosis and apoptosis. Reperfusion of the ischaemic myocardium results in cardiac dysfunction and infarction. 3 Stimulation of α- and β-ARs in the ischaemic heart have variable and inconsistent effects depending on when the agonist is applied. This review describes the different effects of stimulation of the three established β-AR subtypes (β1-, β2- and β3-ARs) either before ischaemia (preconditioning) or during ischaemia and reperfusion of the heart (postconditioning). 4 Brief periods of ischaemia preceding a major ischaemic episode can have a protective effect against post-ischaemia–reperfusion damage, known as ischaemic preconditioning. This review considers the role of endogenous catecholamines released during preconditioning and the nature of the adrenoceptor subtypes that mediate these effects. The clinical significance of this to the use of β-AR antagonists is considered. 5 The transduction pathways and effects on apoptosis of the cardioprotective and deleterious effects of AR activation are considered. 6 This commentary reviews the literature and attempts to bring together a unified synopsis of the effects of adrenoceptor stimulation in myocardial ischaemia and the potential clinical relevance.

Notes: 1 The characteristics of semicarbazide-sensitive amine oxidase (SSAO) are reviewed and the unknown physiological or pathological role of this enzyme emphasized. 2 The various mechanisms of action proposed for the vasodilator drug hydralazine are considered. In particular, the inhibitory action on various enzymes, related or not to cardiovascular function, are discussed. 3 Studies linking inhibition of SSAO to hydralazine hypotension are reviewed and a general hypothesis relating both actions is presented. The hypothesis postulates that (a) vascular SSAO is involved in the regulation of vascular tone, and (b) hydralazine vasodilation is the consequence of vascular SSAO inhibition. 4 Evidence supporting these postulates is presented and vascular SSAO inhibition is proposed as a novel mechanism of vasodilation.

Notes: 1 The regulation by angiotensin II (Ang II) formed locally on nerve-stimulated purinergic and adrenergic components of double-peaked vasoconstrictions in the canine splenic artery and Ang II receptor subtypes involved were investigated. 2 The perfusion of the precursor angiotensin I (Ang I, 0.1–1 nm) did not affect the vasoconstrictor responses to noradrenaline (NA, 0.03–1 nmol) and adenosine 5′-triphosphate (ATP, 0.03–1 μmol). The second component vasoconstrictor response to nerve stimulation was dose dependently potentiated by Ang I (0.1–1 nm). The first peaked constriction was slightly, but insignificantly increased. The potentiating effects of Ang I were abolished by KRH-594 (10 nm), a selective AT1 receptor antagonist, but not by PD 123319 (1–10 nm), an AT2 receptor antagonist. KRH-594 (10 nm) or PD 123319 (10 nm) never affected the vasoconstrictions to either NA or ATP. 3 The treatment with KRH-594 (1–10 nm) produced a greater inhibition on the second peaked response than the first one, although both of them were dose dependently inhibited. PD 123319 (1–10 nm) did not affect the vasoconstrictor responses induced by nerve stimulation. 4 Inhibition of angiotensin-converting enzyme with 10 nm enalaprilat reduced the second peaked response, having no significant inhibition on the first peaked response. A higher dose of enalaprilat (100 nm) produced a greater inhibition of the second peak than the first one. It reduced the second peak by approximately 65%, while the first peak was decreased approximately 35%. After treatment with enalaprilat, Ang I (1 nm) failed to enhance the neuronal vascular response. Enalaprilat at doses used did not affect the vasoconstrictions to either NA or ATP. 5 The present results indicate that endogenously generated Ang II may produce a more marked potentiation of adrenergic transmission than purinergic transmission via activation of prejunctional AT1 receptors.

Notes: 1 The aim of this study was to investigate the co-localization of histamine and dopamine-β-hydroxylase in the superior cervical ganglion of guinea-pig and release of histamine from cardiac sympathetic terminals in guinea-pig isolated atrium. 2 Histidine decarboxylase (a histamine-synthesizing enzyme) mRNA signals were detected in the neurones of superior cervical ganglion of guinea-pig by in situ hybridization. The results of double-labelled immunofluorescence further confirmed the co-localization of histamine and dopamine-β-hydroxylase in the large principle neurons and small intensely fluorescent cells in the superior cervical ganglion. The immunoreactivities of both histamine and dopamine-β-hydroxylase were significantly attenuated after 6-hydroxydopamine-induced lesion of sympathetic nerves. 3 The refractory electrical field stimulation caused the release of histamine from cardiac sympathetic terminals of guinea-pig isolated atria (112.14 ± 40.34 ng ml−1), which was significantly attenuated to 35 ± 15.57 ng ml−1 by reserpine pretreatment. Following administering compound 48/80, a mast cell degranulator, electrical field stimulation induced a dramatic increase of endogenous histamine release from isolated atria (303.57 ±72.93 ng ml−1). When compound 48/80 was added to the reserpine-treated atria, the release of histamine induced by field stimulation was decreased to 207.14 ± 76.39 ng ml−1. 4 These results provide novel evidence that histamine co-exists with noradrenaline in sympathetic nerves and might act as a neurotransmitter to modulate sympathetic neurotransmission.

Notes: 1 The aim of the current study was to investigate in HT-29 human colon cancer cell line, the existence of functional receptors for the signalling molecules, noradrenaline (NA), prostaglandin E2 (PGE2), and adenosine-5′-triphosphate (ATP).2 We utilized microphysiometry, which monitors on-line extracellular acidification rate (ECAR) as a measure of cellular metabolic activity, and how this variable is altered by signalling molecules.3 Challenge with NA (5.9 μm) resulted in an increase in ECAR by approximately 24% of basal.4 PGE2 (0.0284, 0.284 and 2.84 μm) hardly affected ECAR.5 ATP (100 μm) elicited a biphasic effect on ECAR (increase and decrease in ECAR by about 58 and 10% of basal, respectively).6 HT-29 cells were shown to express COX-2 by immunocytochemistry.7 These data suggest the presence of functional receptors for NA and ATP, but not for PGE2 in HT-29 human colon cancer cell line.

Notes: 1 Cardiac vagal outflow is the major factor determining the magnitude of heart rate (HR) variability analysed by traditional time and frequency domain methods. New analysis techniques, such as fractal and complexity methods, have been developed to probe non-linear features in HR behaviour that may not be detectable by traditional methods.2 We investigated the effects of vagal blockade (glycopyrrolate i.v. 5 μg kg−1 h−1 for 2 h, n = 8 vs. unmedicated control group, n = 8) and various breathing patterns (n = 12) on two non-linear measures of HR variability – detrended fluctuation analysis (DFA) and approximate entropy (ApEn) – in healthy male volunteers.3 Glycopyrrolate decreased the mean (±SD) ApEn from 1.46 ± 0.18 to 0.85 ± 0.24 (P = 0.001 in comparison with the control group), and increased the short-term (α1) and intermediate-term (α2) fractal scaling exponents of DFA, α1 from 0.96 ± 0.19 to 1.43 ± 0.29 (P = 0.003) and α2 from 1.13 ± 0.10 to 1.34 ± 0.14 (P 〈 0.001).4 Decrease in fixed respiration rate from 15 to 6 breaths min−1 increased α1 from 0.83 ± 0.25 to 1.18 ± 0.27 (P 〈 0.001), but decreased α2 from 0.88 ± 0.09 to 0.45 ± 0.17 (P 〈 0.001) and ApEn from 1.26 ± 0.12 to 1.10 ± 0.14 (P = 0.028). Rapid breathing (24 min−1) had no influence on these non-linear measures of HR variability. Hyperventilation (15 min−1, tidal volume increased voluntarily by 0.5 l) decreased α1 from 0.83 ± 0.25 to 0.66 ± 0.28 (P = 0.002) but did not affect α2 or ApEn.5 To conclude, vagal blockade alters the fractal scaling properties of R-R intervals (α1, α2) and reduces the complexity (ApEn) of HR behaviour. Both the fractal and complexity measures of HR variability can also be influenced by changes in the breathing pattern.

Notes: 1 Inflammatory bowel disease (IBD) is a condition that involves proinflammatory cytokines such as interleukins 1β and 6 (ILs). In this disease, it has been shown that an abnormal microcirculatory system is implicated. 2 Therefore, the effects of in vivo treatment for three days with interleukins 1β and 6 were investigated on rat isolated mesenteric vascular bed (MVB). 3 A significant concentration-dependent increase in vascular response to noradrenaline (NA) was found, with a significant difference in Emax between control (93.01 ± 16.78 mmHg) and treated preparations (137.91 ± 5.20 mmHg). Endothelin-1(ET-1) induced a significantly greater increase of perfusion pressure in treated rats in comparison with control rats at the highest concentration used (0.1 μm). 4 The concentration-dependent decrease of perfusion pressure induced by acetylcholine (ACh) in MVB precontracted with NA was significantly reduced in specimens from treated rats in comparison with control rats, with a significant difference in Emax between control and treated preparations. 5 Perivascular nerve stimulation (PNS) evoked contractions with no difference between treatments. Similarly, no difference in relaxant effect was found after PNS in specimens precontracted with NA, in the presence of guanethidine. 6 These findings indicate that the precocious inflammation acts only at postsynaptic level, facilitating vascular contraction. These data seem to support the hypothesis that vascular dysfunction caused by overproduction of ILs may contribute, among other immunological factors, to vasculitis in IBD that leads to intestinal ischaemia through vasoconstriction.

Notes: 1 The present study was designed to analyse the possible involvement of V1- and V2-receptors in vasopressin (AVP)-induced facilitation of the sympathetic nervous system. Furthermore, we aimed to determine whether the site of facilitation by AVP is located pre- or postsynaptically. 2 Electrical field stimulation (EFS) was applied on the rat mesteric artery to activate the sympathetic nervous system. In addition, we evaluated the direct vascular effects of AVP. The postsynaptic effect of AVP on the sympathetic nervous system was investigated by exposing the vessels to exogenous noradrenaline. These experiments were performed in the absence or presence of selective V1 and V2 receptor antagonists SR 49059 and SR 121463, respectively. Desmopressin was applied as a selective V2 agonist. 3 The direct vasoconstrictor effect of AVP was antagonized by SR 49059 and not by SR 121463. Desmopressin neither showed any direct vasoconstrictor effect nor produced vasodilatation after a precontraction induced by noradrenaline (10 μm). The EFS-induced rise in vascular tone could be increased by a sub-pressor concentration of AVP. This fascilitation could be antagonized by SR 49059, but not by SR 121463. Desmopressin did not influence the increase in vascular tone during EFS. Vasoconstriction induced by exogenous noradrenaline could be facilitated by a sub-pressor concentration of AVP and this selective postsynaptic effect could be antagonized by V1-receptor blockade. 4 In conclusion, the AVP-induced facilitation of the sympathetic nervous system is completely V1-receptor dependent and at least partly postsynaptically mediated.

Notes: 〈list xml:id="l1" style="custom"〉1To validate the relationship between the dopaminergic, opioidergic and cholinergic nervous systems, we evaluated the effect of domperidone, a dopamine (D2) antagonist, on the opioid system in myenteric plexus-longitudinal muscle preparation isolated from the guinea-pig ileum.2One micromolar of domperidone did not affect the 0.1 Hz-evoked (duration 0.5 ms, maximum intensity) twitch response, but concentration dependently inhibited the twitch response between concentrations of 2 and 20 μm, and the inhibition was maximum after 20–30 min at the highest concentration used (20 μm).3 Acetylcholine-evoked contraction on basal tension was also not inhibited by 1 μm domperidone, but the contraction was concentration dependently inhibited at concentrations of 10–100 μm in a non-competitive manner.4One micromolar of domperidone, however, increased post-tetanic twitch inhibition, an indicator of the release of endogenous opioids. This increase was completely antagonized by 1 μm naloxone.5Twitch inhibition induced by dynorphin 1–13 (0.1–10 nm) was not affected by 1 μm domperidone, but increased the maximum twitch inhibition caused by morphine (0.1–1 μm).6These results might reflect the existence of an interaction between the dopaminergic and opioidergic system without the inhibition of the cholinergic system. Dopamine antagonists increased opioid action, an action that may depend more on the increased release of endogenous opioids than on supersensitivity of the opioid receptor.

Notes: 1 The present study compared the effect of the administration of tachykinin NK1- and NK2-receptor antagonists alone and in combination on exogenous and endogenous tachykinin-induced contractions using three different guinea-pig airway preparations: isolated bronchus, isolated perfused lung and in vivo. 2 In the isolated bronchi, the tachykinin NK1-receptor antagonist CP 99994 (0.01–1 μm)produced concentration-dependent inhibition of contractions induced the tachykinin NK1-receptor agonists substance P (SP) and [Met-OMe11] SP ([Met-OMe11]SP), whereas the tachykinin NK2-receptor antagonist SR 48968 (0.1 μm) had no effect. SR 48968 (0.001–0.01 μm)concentration-dependently inhibited contractions induced by the tachykinin NK2-receptor agonists neurokinin A (NKA) and [β-Ala8]-neurokinin A (4–10) ([βAla8]-NKA) whereas CP 99994 (0.1 μm) did not inhibit the contractions. The contractile activity of capsaicin, an agent that releases endogenous tachykinins from sensory C-fibres, was inhibited in a concentration dependent manner by SR 48968 (0.001–0.03 μm) but not by CP 99994 (0.1 μm). Combination of CP 99994 and SR 48968 caused increased inhibitory effects on the concentration–response curves to SP, [Met-OMe11]SP, NKA, [β-Ala8]-NKA and capsaicin. 3 In isolated perfused lungs, SR 48968 concentration (0.01–10 μm) dependently inhibited NKA-, [β-Ala8]-NKA- and capsaicin-induced bronchoconstriction whereas CP 99994 (30 μm) had no effect on SP-, NKA-, [β-Ala8]-NKA- and capsaicin-induced bronchoconstriction. Combination of inactive concentrations of CP 99994 and SR 48968 produced an increased inhibitory effect on all previous stimuli-induced bronchoconstriction. 4 In in vivo guinea-pig studies, intravenous and oral pretreatment with SR 48968 (0.01–1 mg kg−1 i.v. and 0.1–3 mg kg−1 p.o., respectively), but not with CP 99994 (1 mg kg−1 i.v. and 0.3–30 mg kg−1 p.o., respectively), produced a dose-dependent inhibition of the bronchoconstrictor responses induced by NKA, [β-Ala8]-NKA and capsaicin. CP 99994 intravenously (0.3 mg kg−1) and orally (3–10 mg kg−1) inhibited SP-induced bronchoconstriction only. Intravenous and oral low dose combinations of CP 99994 and SR 48968 produced an increased inhibition of SP-, NKA-, [β-Ala8]-NKA- and capsaicin-induced bronchoconstriction, respectively. 5 The present data indicate that combined tachykinin NK1- and NK2-receptor antagonist treatment compared with single antagonist treatment, using CP 99994 and SR 48968, produced an augmented blockade of tachykinin NK1-, NK2- and capsaicin-mediated contractions in guinea pig airways. These findings support the hypothesis that a dual NK1- and NK2-receptor antagonist may provide an advantage over single activity tachykinin NK1- or NK2-receptor antagonists in pulmonary obstructive diseases.

Notes: 1 This study examined the potentiating effects of competitive antagonists of the adrenergic alpha2 receptors and of phenoxybenzamine (POB) an irreversible antagonist, on the stimulation-induced efflux of [3H]-noradrenaline in arterial tissue of rabbit. This was done to determine if the lack of concordance of efflux potentiation by antagonists with the expectations of presynaptic negative feedback theory can be attributed to increasingly successful competition from rising perineuronal transmitter concentrations, when stimulation parameters are increased, in the presence of a fixed concentration of competitive antagonist. 2 Tissues were stimulated with a fixed pulse number and frequency, to rule out confounding factors, and major alterations in the concentration of released transmitter were achieved through variations in the pulse duration. 3 Rauwolscine potentiated transmitter release less at the longest, rather than at the shortest pulse duration, and showed a potentiation of release that was indifferent to the quantities of released transmitter. This was also seen with POB although it binds covalently to the presynaptic receptor. 4 Noradrenaline inhibited stimulation-induced transmitter release confirming the presence of presynaptic alpha inhibitory sites. 5 Yohimbine potentiated transmitter release the same as did rauwolscine and POB, and protected the relevant sites against POB potentiation, confirming site identity. The combination of POB and rauwolscine had no greater effect than did either alone certifying that they acted similarly and that maximally effective concentrations of each were used. 6 Consequently, noradrenaline breakthrough of presynaptic receptor blockade does not explain the non-conforming observations made with competitive antagonists in tests of presynaptic theory.

Notes: 1 One reason why rabbit jejunum is suitable for studying the mechanisms underlying the actions of the various neurotransmitters and their interactions is its spontaneous motility. The main regulator of spontaneous motility is the cholinergic system. How the cholinergic system regulates the spontaneous activity in the rabbit jejunum and how it affects the inhibitory action of α- and β-adrenoceptor agonists remains unclear. 2 We studied the influence of the cholinergic system and apamin-sensitive Ca2+-activated K+ channels on spontaneous contractions in the rabbit jejunum and on the inhibitory effects ofα1- and β-adrenoceptor agonists. 3 In naïve tissues, atropine (ATR, 7.4 × 10−8 m) and tetrodotoxin (8 × 10−8 m) almost completely inhibited – to a similar extent – the amplitude of spontaneous activity. Despite the presence of ATR or TDX, tissue contraction gradually recovered to about 50% of the baseline amplitude within 5–10 min. When ATR or TDX, respectively, were added to the TDX- or ATR-treated tissues, the recovered activity decreased weakly but significantly. After washout and a 45-min rest the contraction amplitude returned to baseline values. A further exposure to ATR or TDX reduced the contraction to a level significantly lower than the one obtained after TDX or ATR added 5 min after ATR or TDX, respectively. In preparations prestimulated for 10 min with acetylcholine (ACh), ATR abolished the TDX-resistant recovered spontaneous activity. 4 Adrenaline (ADR, 0.5–5 × 10−7 m) and phenylephrine (PHE, 1–10 × 10−7 m) inhibited tissue motility in naïve and in ATR- and in TDX-exposed preparations. But whereas in naïve preparations the α1-adrenoceptor antagonists completely antagonized inhibition induced by both drugs, in ATR- and TDX-exposed tissues they did so only partially for ADR. Agonist-induced inhibition had a rapid onset but rapidly faded; pendular movements took significantly longer to recover in ATR- and TDX-treated tissues than in naïve tissues. In tissues exposed for 2 min to ADR (0.5–5 × 10−7 m) or PHE (1–10 × 10−7 m), washout or addition of α1-adrenoceptor antagonists caused an immediate short-lasting increase in contraction amplitude. 5 Apamin (APAM, 5 × 10−9 m) caused a rapid and persistent increase in the amplitude of contractions. It also blocked the inhibitory responses to ADR and PHE, and removed washout-induced contractions. The APAM-induced increase in the contraction amplitude correlated with the increase obtained by washing out ADR or PHE. 6 Isoprenaline (at concentrations up to 2.8 × 10−7 m) produced no inhibitory response in naïve tissues, but it invariably blocked (at a concentration of 0.7 × 10−7 m) the recovered spontaneous activity (and sometimes depressed muscletone) in tissues exposed to ATR or TDX. Neither propranolol (3.4 × 10−7 m) nor APAM (5 × 10−9 m) counteracted these inhibitory effects. 7 These results indicate that spontaneous motility in the rabbit jejunum is predominantly mediated by neuronal release of ACh and by some other unidentified neuronal activity. Released ACh inhibits myogenic activity and strongly antagonizes β-adrenoceptor-induced APAM-insensitive inhibition but leaves α1 agonist-induced APAM-sensitive inhibition unchanged.

Notes: 1 This study used contractility methods with the portal veins of 5- and 14-week-old Wistar–Kyoto normotensive rats (WKY) and spontaneously hypertensive rats (SHRs). The SHRs are prehypertensive at 5 weeks. 2 The first part of our study was to determine whether the responsiveness to isoprenaline and forskolin was altered in the maturation of portal veins from normo- and prehypertensive rats. The responses to forskolin were similar on the portal veins of 5- and 14-week-old WKY and SHRs. 3 The sensitivity and maximum responses to isoprenaline were similar on portal veins of 5- and 14-week-old WKY. The sensitivity and maximum responses to isoprenaline were lower on the portal veins of 5-week-old SHRs (pD2 = 8.25, maximum = 85%) than age-matched WKY (pD2 = 8.79, maximum = 96%); these differences are not caused by hypertension. At 14 weeks, the sensitivity was similar (WKY pD2 = 8.74, SHR pD2 = 8.65) but the maximum responses to isoprenaline were lower on the portal veins SHRs (77%) than WKY (97%). Thus, the sensitivity to isoprenaline increases with the development of hypertension in the SHR portal vein. 4 The second part of the study was to determine whether the affinity for isoprenaline at β2-adrenoceptors and the fractional β2-adrenoceptor occupancy–response relationships on the portal vein were altered in maturation from normo- and pre-hypertensive rats. The effects of bromoacetylalprenololmenthane (BAAM), an irreversible β-adrenoceptor blocker, on the isoprenaline responses of 5- and 14-week-old WKY and SHRs were studied. Maturation of the WKY portal vein between 5 and 14 weeks was associated with a loss of affinity for isoprenaline (from pKA of 7.13 to 7.87), and increase in β2-adrenoceptor reserve (from 72 to 92% at the 95% response). There were similar affinity and reserve findings in the maturation of the SHR portal vein. Thus, there are major changes in β2-adrenoceptor structure and reserve in maturation on the portal vein that are irrespective of the development of hypertension.

Notes: 1 It is generally recognized that the vasodilator hydralazine produces hypotension accompanied by baroreflex-mediated tachycardia. In some experimental conditions, however, the accompanying heart rate change is bradycardia, a paradoxical response which has not been satisfactorily explained. The present study examined the possibility of hydralazine-induced bradycardia being mediated by vagal or sympathetic afferents activated by changes in left ventricular pressure. 2 Systolic blood pressure and heart rate responses to hydralazine were recorded in conscious normotensive intact rats by a tail cuff method and compared with responses in animals subjected to previous sino-aortic deafferentation (SAD) to remove the influence of the arterial baroreflex. Responses were also obtained after blockade of myocardial afferent vagal C-fibres with urethane, of efferent vagal impulses to the heart with methylatropine, of positive inotropic effects of hydralazine with atenolol, and of prostanoid sensitization of myocardial nerve fibres with indomethacin. 3 Hydralazine produced hypotension and tachycardia in intact rats, and hypotension and bradycardia in SAD animals. In intact rats, this pattern was not affected by any of the pretreatments, while in SAD rats, all pretreatments reversed the bradycardia to hydralazine. 4 The present results indicate that suppression of the arterial baroreflex by SAD propitiates the appearance of a bradycardiac response to hydralazine. This reaction probably results from activation of a vagal cardiodepressant reflex originating in the heart, as suggested by its blockade by drugs acting at various sites along the reflex arch.