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  • Articles  (18)
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  • Articles  (18)
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  • Springer  (18)
  • American Meteorological Society
  • National Academy of Sciences
  • Wiley-Blackwell  (6)
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  • 1995-1999
  • 1990-1994  (18)
  • 1985-1989
  • 1965-1969
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  • 1
    Electronic Resource
    Electronic Resource
    Identification of propafenone metaboliser phenotype from plasma and urine excretion data (1992)
    Springer
    European journal of clinical pharmacology 42 (1992), S. 111-114 
    Details
    ISSN: 1432-1041
    Keywords: Propafenone ; Debrisoquine ; pharmacogenetics ; phenotype analysis ; metabolism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary The aim of the study was to validate a test based on analyses of urine to identify the propafenone metaboliser phenotype during routine chronic therapy. Twenty seven patients chronically treated with propafenone were studied. A debrisoquine test was performed in 10. Propafenone and its metabolites in plasma and urine were measured by HPLC. Propafenone, 5-hydroxypropafenone and N-depropylpropafenone concentrations in plasma were 1.09, 0.182 and 0.101 ng·ml−1, respectively. Total recovery of the administered dose in urine was 30.7%. Two patients were identified as PM, based on the result of the debrisoquine test (log D/4OHD of 1.26 and 1.36). This finding was confirmed by the propafenone metabolic ratio in urine, but the plasma data did not permit clearcut separation of the phenotypes. Propafenone/5-hydroxypropafenone in plasma was not a good predictor of metabolizer phenotype. Although the number of patients who completed all three tests was limited, it is concluded that analysis of propafenone/5-hydroxypropafenone in urine collected between two consecutive doses at steady-state is more practical than the debrisoquine test and more specific than determining the propafenone/5-hydroxypropafenone ratio in plasma, for identification of the propafenone metaboliser phenotypes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00314930
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  • 2
    Electronic Resource
    Electronic Resource
    Formation and excretion of dipyrone metabolites in man (1992)
    Springer
    European journal of clinical pharmacology 42 (1992), S. 187-191 
    Details
    ISSN: 1432-1041
    Keywords: Dipyrone ; Acetylation phenotype ; metabolism ; pharmacokinetics ; urinary excretion ; metabolite clearance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary The formation and urinary excretion of the dipyrone metabolites, methylaminoantipyrine (MAA), aminoantipyrine (AA), formylaminoantipyrine (FAA) and acetylaminoantipyrine (AAA) were determined following administration of a single oral 1.0 g dose of dipyrone to 12 healthy volunteers. The AAA/AA plasma ratio showed that 3 subjects were slow and 9 were rapid acetylators. Pharmacokinetic parameters were determined separately for each group. A good correlation was found between the plasma and urine AAA/AA ratios. The renal clearance of the four metabolites was similar for both phenotypes. A significant difference in the rate of formation of dipyrone metabolites was found for AA, 0.25 (slow) vs 0.1 ml·min−1·kg−1 (rapid), and for AAA 0.75 (slow) vs 7.53 ml·min−1·kg−1 (rapid). There were comparable differences between slow and rapid acetylators in the AUC and the urinary excretion extrapolated to infinity for AA and AAA. The present results show that the kinetics of dipyrone metabolites in plasma and urine can provide a useful measure of the activity of the enzymes involved in their production.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00278482
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  • 3
    Electronic Resource
    Electronic Resource
    Myocardial fatty acid oxidation during ischemia and reperfusion (1992)
    Springer
    Molecular and cellular biochemistry 116 (1992), S. 103-109 
    Details
    ISSN: 1573-4919
    Keywords: metabolism ; fatty acid ; glucose ; reperfusion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Inhibition of fatty acid oxidation is an early event in myocardial ischemia that most likely contributes to tissue injury by the accumulation of potentially toxic intermediates such as acylCoA and acylcarnitine. After reperfusion both myocardial oxygen consumption and fatty acid oxidation may rapidly recover to preischemic levels, even when contractile function remains depressed. The mechanisms underlying the apparent dissociation between contractile function and oxidative metabolism early during reperfusion are still controversial. In isolated rat hearts subjected to 60 min of no-flow ischemia myocardial oxygen consumption and oxidation of palmitate were lowered during reperfusion by 3 mM of NiCl2 and by 6 µM of ruthenium red. The results provide indirect evidence for the hypothesis that intracellular calcium transport may be involved in the mechanisms responsible for the high oxidative metabolic rate early after reperfusion
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01270576
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  • 4
    Electronic Resource
    Electronic Resource
    A kinetic description of sequential, reversible, Michaelis-Menten reactions: practical application of theory to metabolic pathways (1992)
    Springer
    Molecular and cellular biochemistry 115 (1992), S. 43-48 
    Details
    ISSN: 1573-4919
    Keywords: coupled enzymes ; steady state ; transition times ; metabolism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Equations are presented which describe a linear coupled system of reactions that utilize a single substrate and convert it to product by way of several intermediate enzyme catalysed steps. The present analysis extends previous results by assuming that the enzymes obey reversible Michaelis-Menten kinetics. In order for the system to reach steady state one must assume that the initial substrate concentration and the final product concentration are buffered to a constant value. Using the present analysis it can be shown that the system will not enter a steady state if the maximal velocity of any forward reaction is less than the steady state flux through the system. This condition represents a practical test for determining if a system will enter steady state but is valid only when the rate of the primary enzyme is not affected allosterically be intermediates in the pathway. The equations are used to analyse a portion of the rat liver glycogenic pathway that catalyses the conversion of glucose to fructose 1,6-bisphosphate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00229094
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  • 5
    Electronic Resource
    Electronic Resource
    Possible function of ecdysteroid-22-O-acyltransferase in the larval gut of tobacco budworm,Heliothis virescens (1992)
    Springer
    Journal of chemical ecology 18 (1992), S. 1139-1149 
    Details
    ISSN: 1573-1561
    Keywords: Detoxification ; ecdysteroid ; metabolism ; brush border membrane ; epithelial cell
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract In the larval gut of the tobacco budworm,Heliothis virescens, most ingested ecdysteroids are transformed to ecdysteroid-22-acyl esters by a novel enzyme, ecdysteroid-22-O-acyltransferase. This conversion is different from the normal metabolic pathway in which the compounds are usually transformed to more water-soluble products. Most ecdysteroid-22-O-acyltransferase activity was found in the midgut epithelial-cell membrane and was active only during feeding stages. The activity decreased as the larvae became committed to pupation, and it was not enhanced by feeding ecdysteroids to the fifth-instar larvae. Our preliminary results showed that the esterification was very specific to 22-OH in ecdysteroids. We suggest that detoxification is the major function of ecdysteroid-22-O-acyltransferase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00980069
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  • 6
    Electronic Resource
    Electronic Resource
    Fate of [14C]xanthotoxin (8-methoxypsoralen) in laying hens and a lactating goat (1992)
    Springer
    Journal of chemical ecology 18 (1992), S. 253-270 
    Details
    ISSN: 1573-1561
    Keywords: Xanthotoxin ; 8-methoxypsoralen ; furanocoumarin ; metabolism ; detoxification ; chicken ; goat ; egg ; milk14C radiolabel
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The metabolism of xanthotoxin, a naturally occurring furanocoumarin photosensitizer, was studied in laying hens and a lactating goat treated with single oral doses equivalent to 10 mg xanthotoxin/kg of body weight. Within 48 h, essentially all of the administered radiocarbon was eliminated in the excreta of the laying hens, while in the goat 92% and 3% were excreted in the urine and feces, respectively. Radiocarbon residues in the milk, egg white, and egg yolk were low. Xanthotoxin, 8-hydroxypsoralen (xanthotoxol), 6-(7-hydroxy-8-methoxycoumaryl)-acetic acid (HCA) and 6-(7-hydroxy-8-methoxycoumaryl)-hydroxyacetic acid (HCHA) were identified in the excreta of laying hens. In the goat, xanthotoxin was metabolized to HCA, HCHA, xanthotoxol, 5,8-dihydroxypsoralen, psoralenquinone, 5-hydroxy-8-methoxy-psoralen and 3[5-(6-hydroxy-7-methoxybenzofuryl)]-propanoic acid. Thus, identified metabolites in one or both of these species arose throughO-demethylation, oxidative cleavage of the furan ring, hydroxylation, reduction, oxidation, and hydrolysis of the lactone ring.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00993757
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  • 7
    Electronic Resource
    Electronic Resource
    2-Ketoisocaproate transport in insulin-secreting cells (1992)
    Springer
    Bioscience reports 12 (1992), S. 69-76 
    Details
    ISSN: 1573-4935
    Keywords: pancreatic islets ; HIT-T15 cells ; 2-ketoisocaproate transport ; metabolism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The transport of the nutrient secretagogue 2-ketoisocaproate (KIC) was studied in isolated rat pancreatic islets and in the HIT-T15 insulinoma cell line using an oil-filtration technique. In both islets and HIT-T15 cells, KIC uptake was a slow process, not reaching equilibrium within 10 min KIC transport was not dependent upon Na+ in the medium, was not inhibited by α-cyano-4-hydroxy-cinnamate nor by 2-amino-2-norborane carboxylic acid (BCH) and did not appear to be electrogenic. Evidence was obtained to suggest that KIC uptake occurred via passive diffusion into the cell of the undissociated acid species. This possibility was supported by the apparent unsaturability of KIC uptake in HIT-T15 cells. Addition of 10–30 mM KIC to dispersed islets cells or HIT-T15 cells produced a rapid intracellular acidification. In islets, the rate of transport of 10 mM KIC was comparable with oxidation rate of the keto-acid suggesting that uptake could be rate-limiting factor for KIC oxidation and thus stimulated insulin release. However, in HIT-T15 cells, the rate of uptake of KIC greatly exceeded the oxidation rate. The low rate of KIC oxidation could explain the poor secretory response of HIT-T15 cells to KIC
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01125829
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  • 8
    Electronic Resource
    Electronic Resource
    Nasal Absorption of Leucine Enkephalin in Rats and the Effects of Aminopeptidase Inhibition, as Determined from the Percentage of the Dose Unabsorbed (1992)
    Springer
    Pharmaceutical research 9 (1992), S. 1362-1364 
    Details
    ISSN: 1573-904X
    Keywords: nasal ; absorption ; enkephalin ; peptide ; metabolism ; inhibitor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1015882006897
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  • 9
    Electronic Resource
    Electronic Resource
    Effect of Isoflurane Anesthesia on Antipyrine Pharmacokinetics in the Rat (1992)
    Springer
    Pharmaceutical research 9 (1992), S. 1515-1517 
    Details
    ISSN: 1573-904X
    Keywords: isoflurane ; anesthesia ; antipyrine ; metabolism ; pharmacokinetics ; rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1015835618709
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  • 10
    Electronic Resource
    Electronic Resource
    Mechanism and Site Dependency of Intestinal Mucosal Transport and Metabolism of Thymidine Analogues (1992)
    Springer
    Pharmaceutical research 9 (1992), S. 326-331 
    Details
    ISSN: 1573-904X
    Keywords: thymidine analogues ; intestinal absorption ; mechanism ; metabolism ; colonic absorption ; enhancement ; mixed micelle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract This study has been undertaken to investigate the mechanisms of intestinal mucosal transport and metabolism of thymidine analogues and to identify any optimal site(s) of the rat intestine particularly involved in the absorption of thymidine analogues. The intestinal absorption of 3′-azido-3′-deoxythymidine (AZT) was studied at three initial concentrations in four segments of the rat intestine using an in situ recirculating perfusion technique. Disappearance of AZT followed first-order kinetics throughout the gastrointestinal (GI) tract at all tested concentrations. The apparent first-order rate constants were found to be relatively invariant over a broad range of concentrations from 0.01 to 1.0 mM. Corrected for the length of each segment, the apparent permeability (P app) of AZT was 3.01 ± 0.32 × 10−5 cm/sec (mean ± SE) in the duodenum, 2.06 ± 0.24 × 10−5 cm/sec in the upper jejunum, 0.76 0.13 × 10−5 cm/sec in the combined lower jejunum and ileum, and 0.32 ± 0.10 × 10−5 cm/sec in the colon, which indicated that intrinsic absorptivity was greater in the upper GI tract than in the lower portions possibly due to the differences in surface area for absorption. No AZT metabolite appeared in any part of the GI tract. On the other hand, thymidine and other analogues, i.e., 5-iodo-2′-deoxyuridine and 2′-deoxyuridine, were rapidly metabolized into nucleobase and sugar in the upper GI tract, whereas in the colon no metabolite appeared. A free 3′-OH group appears to be necessary for the metabolism (catabolism) of thymidine analogues in the rat intestine mainly by pyrimidine nu-cleoside phosphorylase. Finally, bile salt-acylcarnitine mixed micelles appeared to be an effective adjuvant in promoting colonic absorptions of AZT and phenol red. The use of mixed micelles increased the apparent permeabilities of AZT in the colon by a factor of 5.4, and for phenol red the permeability increased from a negligible value to 1.76 × 10−5 cm/sec. Since the absorptions of both AZT and phenol red were enhanced by mixed micelles, a paracel-lular transport pathway may be involved.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1015882617066
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  • 11
    Electronic Resource
    Electronic Resource
    Inhibition of Hepatic and Cutaneous Biotransformation of Resorufin Ethers Following Intraperitoneal Administration of 1-Aminobenzotriazole (1992)
    Springer
    Pharmaceutical research 9 (1992), S. 1099-1102 
    Details
    ISSN: 1573-904X
    Keywords: 1-aminobenzotriazole ; metabolism ; inhibition ; resorufin ; skin ; liver ; microsomes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1015827100111
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  • 12
    Electronic Resource
    Electronic Resource
    Transport of Thyrotropin Releasing Hormone in Rabbit Buccal Mucosa in Vitro (1992)
    Springer
    Pharmaceutical research 9 (1992), S. 1113-1122 
    Details
    ISSN: 1573-904X
    Keywords: thyrotropin releasing hormone ; buccal mucosa ; metabolism ; permeability ; in vitro tissue integrity ; transport pathways ; rate-limiting barrier
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The transport of thyrotropin releasing hormone (TRH) in rabbit buccal mucosa in vitro has been investigated with respect to (a) rate and type of metabolism of TRH on mucosal and serosal sides of buccal mucosa, (b) mechanism of TRH transport including charge effect on its permeability, and (c) pathway and rate-limiting regions of TRH movement. In addition, the integrity of excised buccal mucosa has been evaluated for purposes of in vitro solute diffusion experiments using tissue ATP level data, transmission electron microscopy, and TRH transport kinetic data. The results indicate that excised rabbit buccal mucosa can be used for TRH diffusion studies for approximately 6 hr. In addition, TRH apparently traverses buccal mucosa by simple diffusion with a steady-state permeability of about 10−7 cm/sec, and this permeability is independent of pH. Moreover, the primary pathway appears to be via the intercellular space in the rate-limiting barrier, i.e., the upper 50 µm of the epithelium. Finally, TRH is degraded predominantly by deamidase activity, which is followed by, to a lesser degree, carboxypeptidase metabolism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1015883217858
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  • 13
    Electronic Resource
    Electronic Resource
    Enhanced Delivery of 5-Iodo-2′-Deoxyuridine to the Brain Parenchyma (1992)
    Springer
    Pharmaceutical research 9 (1992), S. 1173-1176 
    Details
    ISSN: 1573-904X
    Keywords: 5′-ester prodrugs ; 5-iodo-2′-deoxyuridine ; distribution ; brain uptake ; metabolism ; competitive inhibition ; sustained brain levels
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract 5′-Ester derivatives of 5-iodo-2′-deoxyuridine (IDU) with varying degrees of lipophilicity were examined to evaluate the effectiveness of lipophilic ester prodrugs for enhanced and sustained delivery of IDU to the brain parenchyma. Approximately 1.0% (1.0 ± 0.19; n = 4) of the total radioactivity was found in the brain at 30 min following intravenous administration of the lipophilic benzoyl-5′-ester of 125I-labeled IDU, whereas IDU per se yielded only 0.01% (0.01 ± 0.06; n = 4). Since the IDU 5′-esters generated significantly higher levels of IDU in the brain, an HPLC analysis of IDU in the presence of 5′-esters and the metabolite 5-iodouracil was developed to characterize IDU uptake in the brain. The drug was detected at levels of 6.6 and 9.5 µg/g of brain tissue at 3 hr following intravenous administration of valeryl and benzoyl IDU, respectively, at a dose level of 40 mg/kg IDU equivalent each. IDU, on the other hand, when injected at a similar dose level, produced concentration levels below 0.01 µg/g of brain tissue, which was too low to be detected accurately by the HPLC assay. These results suggest that the 5′-ester derivatives cross the blood-brain barrier effectively and generate significantly higher brain levels of the parent drug in the brain parenchyma. The regenerated hydrophilic drug because of its polarity is “locked in” the brain and is subsequently metabolized by pyrimidine phosphorylase to 5-iodouracil. A higher concentration of IDU was generated following administration of the benzoyl ester probably because the ester itself is slowly hydrolyzed by the brain cholinesterases, thereby competitively inhibiting the metabolism of IDU to 5-iodouracil by brain pyrimidine phosphorylase. 5′-Benzoyl IDU appears to be a promising bioreversible analogue which can provide enhanced and sustained delivery of IDU to the brain parenchyma.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1015803922401
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  • 14
    Electronic Resource
    Electronic Resource
    Disposition, Bioavailability, and Serum Protein Binding of Pentachlorophenol in the B6C3F1 Mouse (1992)
    Springer
    Pharmaceutical research 9 (1992), S. 1053-1057 
    Details
    ISSN: 1573-904X
    Keywords: pentachlorophenol ; tetrachlorohydroquinone ; toxicokinetics ; metabolism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The toxicokinetics of pentachlorophenol (PCP) were studied in B6C3F1 mice, a strain in which PCP was previously found to be carcinogenic. In a crossover design, doses of 15 mg/kg were given intravenously (bolus) and orally (gastric intubation) to six animals. Concentrations of PCP in blood, urine, and feces were measured by capillary gas chromatography with electron-capture detection. After intravenous administration, the values of clearance and volume of distribution were 0.057 ± 0.007 L/hr/kg and 0.43 ± 0.06 L/kg, respectively. These two parameters exhibited low intermouse variability (coefficients of variation 〈14%). The elimination half-life was 5.2 ± 0.6 hr. After oral administration, the PCP peak plasma concentration (28 ± 7 µg/ml) occurred at 1.5 ± 0.5 hr and absorption was complete (bioavailability = 1.06 ± 0.09). The elimination half-life was 5.8 ± 0.6 hr. Only 8% of the PCP dose was excreted unchanged by the kidney. PCP was primarily recovered in urine as conjugates. A portion of the dose was recovered in urine as the mutagen, tetrachlorohydroquinone (5%) (TCHQ), and its conjugates (15%). For both PCP and TCHQ, sulfates accounted for 90% or more of the total conjugates (glucuronides and sulfates).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1015810629245
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  • 15
    Electronic Resource
    Electronic Resource
    Metabolism, Distribution, and Transdermal Permeation of a Soft Corticosteroid, Loteprednol Etabonate (1992)
    Springer
    Pharmaceutical research 9 (1992), S. 1275-1278 
    Details
    ISSN: 1573-904X
    Keywords: soft corticosteroid ; loteprednol etabonate ; metabolism ; tissue distribution ; transdermal permeability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The soft corticosteroid, loteprednol etabonate (chloromethyl 17α-ethoxycarbonyloxy-11β-hydroxy-3-oxoandrosta-1,4-diene-17β-carboxylate), I, was designed based on the “inactive metabolite approach.” Accordingly, I should be metabolized by hydrolysis to the corresponding inactive cortienic acid derivative, II. The in vitro and in vivo metabolism of I indeed yielded mainly this inactive metabolite, which is more hydrophilic and thus readily eliminated from the body. Relatively high levels of I were found in tissues after intravenous administration of the drug in rats. The permeability of I through hairless mouse skin was comparable to what has been found for related “hard” steroids, without significant metabolism taking place in the skin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1015849132396
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  • 16
    Electronic Resource
    Electronic Resource
    Metabolism of Testosterone During in Vitro Transport Across CACO-2 Cell Monolayers: Evidence for β-Hydroxysteroid Dehydrogenase Activity in Differentiated CACO-2 Cells (1992)
    Springer
    Pharmaceutical research 9 (1992), S. 1290-1294 
    Details
    ISSN: 1573-904X
    Keywords: CACO-2 ; cell culture ; unstirred water layer ; metabolism ; testosterone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Testosterone has previously been used as a model compound for the determination of unstirred water layer thickness in the CACO-2 transport model. We have found, however, that testosterone is metabolized during in vitro transport across the CACO-2 cell monolayers. This suggests that testosterone is not an ideal model substance. Testosterone is metabolized to androstenedione, indicating the formation of 17-β-hydroxysteroid dehydrogenase by differentiated CACO-2 cells. No reverse metabolism is observed, thus androstenedione is considered superior to testosterone for determination of unstirred water layer thickness in the CACO-2 system. Permeability coefficients for testosterone and androstenedione obtained under identical transport conditions were 66 (±7) * 10 −6 (n = 26) and 84 (±7) * 10−6 (n = 9) cm/sec, respectively. The unstirred water layer thicknesses at different agitation rates are determined for the CACO-2 transport model used in our laboratory utilizing androstenedione as a model compound. The system is capable of controlling the water layer thickness from about 200 to 1000 µm.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1015805317375
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  • 17
    Electronic Resource
    Electronic Resource
    Pharmacokinetic and Metabolic Disposition of p-Chloro-m-xylenol (PCMX) in Dogs (1992)
    Springer
    Pharmaceutical research 9 (1992), S. 677-682 
    Details
    ISSN: 1573-904X
    Keywords: p-chloro-m-xylenol (PCMX) ; metabolism ; pharmacokinetics ; conjugated metabolites
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The pharmacokinetic and metabolic profile of p-chloro-m-xylenol (PCMX) was studied in healthy mongrel dogs after intravenous and oral administration of single doses of 200 and 2000 mg of PCMX, respectively. Calculation of pharmacokinetic parameters was based on compartmental and noncompartmental methods. The mean pharmacokinetic parameters of elimination half-life and mean residence time were 1.84 and 1.69 hr, respectively. The apparent volume of distribution at steady state was estimated to be 22.4 liters, and the plasma clearance was 14.6 liters/hr. The bioavailability of PCMX was 21%, indicating low absorption for this drug. PCMX's metabolite data show that a presystemic elimination process (first-pass effect) is also occurring. PCMX plasma concentrations after intravenous administration of 500-, 200-, and 100-mg doses were found to be proportional to the dose given, demonstrating that the pharmacokinetic profile of PCMX is linear over the dose range studied. Biotransformation studies showed that urinary excretion was not the major route for rapid elimination of unchanged PCMX and almost all material excreted in urine was associated with the conjugated species (glucuronides and sulfates). Statistical significant differences were not found (P 〉 0.05) between the percentages excreted in urine of PCMX and its conjugated metabolites after intravenous and oral administration. The percentages excreted in urine after iv and oral doses of unchanged PCMX were, respectively, 0.45 and 0.37; total conjugates, 46.3 and 43.3; sulfates, 38.1 and 33.2; and glucuronides, 8.2 and 10.2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1015814513373
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  • 18
    Electronic Resource
    Electronic Resource
    Brain Parenchymal Metabolism of 5-Iodo-2′-Deoxyuridine and 5′-Ester Prodrugs (1992)
    Springer
    Pharmaceutical research 9 (1992), S. 1048-1052 
    Details
    ISSN: 1573-904X
    Keywords: 5-iodo-2′-deoxyuridine ; 5′-ester prodrugs ; metabolism ; brain ; cytosolic fraction ; esterase activity ; phosphorylase activity ; competitive inhibition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In an attempt to generate derivatives of 5-iodo-2′-deoxyuridine (IDU) with enhanced blood-brain barrier (BBB) permeability, a series of 5′ ester prodrugs of IDU was synthesized and their metabolism studied in rat brain homogenate and its different subcellular fractions. The rate of hydrolysis was dependent on the steric and polar nature of the ester substituent. Ester hydrolyzing activities were associated primarily with the cytosolic fraction and were due mainly to the presence of cholinesterases as confirmed by inhibition experiments performed with different esterase inhibitors. The metabolism of IDU to 5-iodouracil (5-IU) by the cytosolic fraction, in the presence and absence of specific pyrimidine nucleoside phosphorylase inhibitors, also suggests that there are two specific enzyme systems catalyzing two different metabolic processes. IDU 5′-esters competitively inhibit the metabolism of IDU and the inhibitory effect depends on the affinity of a particular ester toward the enzyme and also on the rate by which the ester itself undergoes hydrolysis. In the absence of any 5′-ester, 95% IDU was metabolized within 6 hr. However, in the presence of an eightfold molar excess of butyryl-IDU, the hydrolysis of IDU was completely inhibited over a 6-hr time period.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1015858512407
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