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  • 1
    ISSN: 0300-9629
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0305-0491
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology
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  • 3
    ISSN: 0305-0491
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology
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  • 4
    ISSN: 1432-0827
    Keywords: Calcitriol ; Ca2+ absorption ; Vitamin D receptor ; Piglets ; Pseudo vitamin D deficiency ; Rickets
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary The role of 1,25-dihydroxycholecalciferol (calcitriol) for intestinal calcium (Ca2+) absorption was studied in newborn (〈1 week old) and weaned piglets (〉6 weeks old). In both groups, normal piglets and piglets suffering from inherited pseudo vitamin D-deficiency rickets, type I (PVDRI) were used. In this inherited disorder, renal production of calcitriol is absent. Plasma samples were assayed for calcitriol and total Ca, and dissociation constants (Kd) and maximum binding capacities (Bmax) of intestinal calcitriol receptors were determined under equilibrium conditions at 4°C. Unidirectional Ca2+-flux rates were measured across stripped duodenal mucosae in Ussing chambers in the absence of electrochemical gradients. The plasma calcitriol concentrations of neonatal (26.5±7.1 pg/ml, n=11; $$\bar x$$ ± SEM) and weaned PVDRI piglets (18.8±5.7 pg/ml, n=8)were unphysiologically low and differed significantly from control animals (83.6±14.8 pg/ml, n=8, and 86.9±9.6 pg/ml, n=11, respectively). However, newborn PVDRI piglets had normal plasma Ca levels at least during the first days of life. They became hypocalcemic and developed clinical symptoms of rickets during the following weeks. In newborn PVDRI and control piglets, Bmax was significantly lower (84±28 fmol/mg protein and 127±55 fmol/mg protein, n=9, respectively) than in weaned piglets (741±82 fmol/mg protein, n=9, and 778±121 fmol/mg protein, n=8, respectively). Significant net Ca2+-fluxes were found in both newborn PVDRI and control piglets (88.8±25.1 nmol · cm-2 · h-1, n=6, and 86.5±10.5 nmol · cm−2 · h−1,n=9, respectively). However, active net Ca2+ absorption was completely absent in weaned PVDRI piglets. These results indicate the presence of vitamin D-independent mechanisms for active intestinal Ca2+ absorption during early postnatal life in pigs.
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  • 5
    ISSN: 1432-136X
    Keywords: Phosphate transport ; Jejunum ; Calcitriol ; Goats
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract This study concerns the uptake of inorganic phosphate into brush-border membrane vesicles prepared from jejunal tissues of either control or Ca-and/or P-depleted goats. The brush-border membrane vesicles showed a time-dependent accumulation of inorganic phosphate with a typical overshoot phenomenon in the presence of an inwardly directed Na+ gradient. The Na+-dependent inorganic phosphate uptake was completely inhibited by application of 5 mmol·l-1 sodium arsenate. Half-maximal stimulation of inorganic phosphate uptake into brush-border membrane vesicles was found with Na+ concentrations in the order of 5 mmol·l-1. Inorganic phosphate accumulation was not affected by a K+ diffusion potential (inside negative), suggesting an electroneutral transport process. Stoichiometry suggested an interaction of two or more Na ions with one inorganic phosphate ion at pH 7.4. Na+-dependent inorganic phosphate uptake into jejunal brush-border membrane vesicles from normal goats as a function of inorganic phosphate concentration showed typical Michaelis-Menten kinetic with V max=0.42±0.08 nmol·mg-1 protein per 15 s-1 and K m=0.03±0.01 mmol·l-1 (n=4, x ±SEM). Long-term P depletion had no effect on these kinetic parameters. Increased plasma calcitriol concentrations in Ca-depleted goats, however, were associated with significant increases of V max by 35–80%, irrespective of the level of P intake. In the presence of an inwardly directed Na+ gradient inorganic phosphate uptake was significantly stimulated by almost 60% when the external pH was decreased to 5.4 (pHout/pHin=5.4/7.4). The proton gradient had no effect on inorganic phosphate uptake in absence of Na+. In summary, in goats Na+ and calcitriol-dependent mechanisms are involved in inorganic phosphate transport into jejunal brush-border membrane vesicles which can be stimulated by protons.
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  • 6
    ISSN: 1432-136X
    Keywords: Key words Renal Pi transport ; P depletion ; Ca depletion ; Renal cortex brush border membranes ; AbbreviationsAP alkaline phosphatase ; BBM brush border membranes ; BBMV brush-border membrane vesicles ; DM dry matter ; Pi inorganic phosphate ; PTH parathyroid hormone ; RT-PCR reverse transcriptase-polymerase chain reaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract In contrast to monogastric species, renal excretion of inorganic phosphate (Pi) in ruminants is low and this could be attributed to an almost complete tubular Pi reabsorption. However, the functional and regulatory basis for this phenomenon has not yet been clarified. Therefore, it was the aim of the present study to characterize the kinetic parameters of the tubular Pi reabsorption system as affected by P or Ca depletion using preparations of renal cortex brush border membrane vesicles (BBMV) from goats and sheep and to compare the data with respective parameters of porcine preparations. Na-dependent Pi uptake into renal cortex BBMV as a function of Pi concentration showed typical Michaelis-Menten kinetic and respective Scatchard plot analysis of the specific Pi uptake revealed linearity indicating the predominant presence of a single type of Pi transporters in the preparations. Under control conditions Vmax values of Na-dependent Pi uptake into BBMV were highest in goats and sheep and lowest in pigs (1.98, 1.39 and 0.95 nmol · mg−1 protein · 10 s−1, respectively). Km values were not different between goats and sheep under all feeding conditions and ranged from between 0.34 mmol · l−1 and 0.55 mmol · l−1 which was three- to five-times higher than that found in pigs (0.11 mmol · l−1). Oligonucleotides derived from rat kidney cortex type IIa Na/Pi cDNA were used for reverse transcriptase-polymerase chain reaction (RT-PCR) in goat, sheep and pig kidney cortex. The products isolated were 768 bp for sheep and pigs and 765 bp for goats, with the respective amino acids sequences, representing a segment of approximately 40% in length of the entire transporter, exhibiting an at least 92% sequence homology between different species. From the results, involvement of type IIa Na/Pi cotransport in tubular Pi reabsorption in small ruminants can be postulated. However, it should not be considered that a potential role of other Pi transport systems be completely be excluded. Interestingly, neither P nor Ca depletion caused significant effects on Na-dependent Pi transport capacities and affinities in goats and sheep. From this, parathyroid-hormone independent regulatory pathways of tubular Pi reabsorption can be assumed.
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  • 7
    ISSN: 1432-136X
    Keywords: Key words Dipeptide transport ; Jejunum ; Pigs ; Ussing chamber ; PepT1
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract  Characteristics of dipeptide transport in pig jejunum were investigated in vitro by applying the Ussing-chamber technique and mucosal uptake studies. Addition of both glycyl-l-glutamine and glycyl-l-sarcosine (20 mmol · l−1) to the mucosal buffer solution significantly increased the short-circuit current by 2.60 ± 0.15 and 1.57 ± 0.20 μeq · cm−2 · h−1, respectively. Concentration-dependent changes in short-circuit current followed Michaelis-Menten kinetics with similar affinity constants for both dipeptides. From unidirectional flux rates for radiolabelled glycyl-l-sarcosine, a net flux rate for glycyl-l-sarcosine of 49.8 ± 6.7 nmol · cm−2 · h−1 was calculated. In mucosal uptake experiments, the apical influx of 14C-labelled glycyl-l-sarcosine into isolated porcine mucosa was pH dependent and significantly inhibited by glycyl-l-glutamine. Moreover, RT-PCR studies with primers derived from rabbit PepT1 identified two PCR fragments of identical size to rabbit PepT1 from pig intestinal mRNA preparations. In conclusion, our studies revealed key features of mammalian intestinal peptide transporters and give evidence for a PepT1-like transporter in the pig jejunum that could significantly contribute to the overall amino acid absorption from the gut.
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  • 8
    ISSN: 1432-136X
    Keywords: Key words Calcium absorption ; Rumen ; Sheep ; Short chain fatty acids ; Ca depletion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract From various in vivo and in vitro studies it has been shown that the rumen represents a significant site of Ca2+ absorption in sheep and goats. It was the aim of the present study to further characterize the underlying mechanisms. Unidirectional flux rates of Ca2+ across rumen wall epithelia of sheep were measured in vitro by applying the Ussing-chamber technique in the absence of electrochemical gradients. Under these conditions, significant Ca2+ net flux rates (Jnet) clearly indicate the presence of active mechanisms for Ca2+ transport. Short chain fatty acids (SCFAs) caused highest stimulation of Ca2+ Jnet (6.3 ± 1.9 nmol · cm−2 · h−1) when used as a mixture of acetate, proprionate and butyrate in physiological proportions (36, 15, 9 mmol · l−1, respectively). The effect of 30 mmol · l−1 butyrate (3.2 ± 0.6 nmol · cm−2 · h−1) was higher than respective amounts of propionate and acetate (0.6 ± 0.8 nmol · cm−2 · h−1 and 0.9 ± 0.8 nmol · cm−2 · h−1, respectively). Eliminating SCFAs resulted in Ca2+ Jnet of 0.4 ± 1.1 nmol . cm−2 . h−1. Addition of Ca channel blocker verapamil (mucosal 1 mmol · l−1) had no significant effect on SCFA-stimulated Jnet of Ca2+, whereas application of Na+/H+ inhibitor amiloride (mucosal 1 mmol · l−1) further enhanced the Ca2+ Jnet by 〉65%. The Ca2+-pump inhibitor vanadate had no significant effect on Jnet of Ca2+. Dietary Ca depletion enhanced calcitriol plasma concentrations but had no effect on active Ca2+ absorption across the rumen wall of sheep. In addition, no effect on active Ca2+ absorption could be observed during early lactation. In conclusion, there is clear evidence for the rumen as a main site for active Ca2+ absorption in sheep. Our results suggest the presence of a Ca2+/H+ exchange mechanism in the apical membrane of rumen epithelial cells which depends on SCFA absorption and which does not seem to be under the control of calcitriol. Basolateral Ca2+ extrusion occurs independently from Ca2+-pump activity and may be accomplished via Na+/Ca2+ exchange.
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  • 9
    ISSN: 1432-136X
    Keywords: Key words Roe deer ; Salivary proteins ; Tannin-binding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract In ruminants, different functions have been ascribed to the different salivary glands according to the feeding type. In this context, possible adaptations of salivary functions were investigated regarding the secretion of various proteins by different types of salivary glands. To yield uncontaminated parotid saliva in large quantities, a non-surgical method has been developed. Parotid gland secretions were collected via endoscopic placement of guide wires into each parotid duct, which were subsequently used for placement of collection catheters. Salivary flow was stimulated by intra-glandular administration of the parasympathomimetic compound pilocarpine-hydrochloride into the parotid gland. Mixed saliva (excluding parotid saliva) was collected into sterile tubes by normal outflow during the sampling of parotid saliva. The total flow volume, flow rate and the content of proteins as well as of several ions (Na+, K+, Ca2+, inorganic phosphate) of both types of saliva were measured in sheep, fallow deer and roe deer. Roe deer secreted the highest amount of total salivary proteins relative to body mass [mg/kg body mass] and the highest relative volume [ml/10 min/kg body mass], both in parotid and mixed saliva, of all ruminant species examined. Additionally, the protein profile and the tannin-binding properties of parotid and mixed saliva in roe deer were investigated. Parotid saliva bound almost twice as much tannin as mixed saliva, underlining the importance of yielding uncontaminated parotid saliva for tannin-binding studies.
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