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Biomedical subjects

S Schenker

Publications and source records attributed to S Schenker.

At least 73 records · Page 4Linked to original sources
PubMed1991

Colchicine clearance is impaired in alcoholic cirrhosis.

Colchicine may have benefit in primary biliary cirrhosis and alcoholic liver disease. It is currently used in patients with impaired liver function, yet little is known about its elimination in such patients. Colchicine clearance in the rat is significantly impaired in various models of liver disease. To study this in human beings, colchicine pharmacokinetics were compared in normal subjects and patients with alcoholic cirrhosis. Colchicine clearance was impaired in the cirrhotic patients. Normal subjects had a mean clearance of 10.65 +/- 1.82 ml/min.kg, whereas cirrhotic patients had a mean clearance of 4.22 +/- 0.45 ml/min.kg (p less than 0.01). The half-life was 57.4 +/- 14.2 min in control subjects vs. 114.4 +/- 19.7 min in cirrhotic patients (p = 0.054). Volume of distribution was not different in the two groups (0.718 +/- 0.1 L/kg in control subjects; 0.716 +/- 0.158 L/kg in cirrhotic patients, p greater than 0.99). No correlation was seen between colchicine clearance and bilirubin, albumin, prothrombin time or Child-Pugh classification, but this may be the result of the small number of patients studied. Based on the values measured, it is estimated that colchicine steady state would change from an average 1.12 ng/ml in normal individuals to 2.82 ng/ml in the cirrhotic patients if 0.6 mg were taken every 12 hr. It is unknown whether this change would be clinically significant. These data show that cirrhosis impairs colchicine clearance and demonstrates that the liver is a major route of colchicine elimination.

Adult↗
PubMed1990

The effect of liver dysfunction on colchicine pharmacokinetics in the rat.

Recent work has shown that colchicine may benefit patients with primary biliary or alcoholic cirrhosis. However, very little is known about its pharmacokinetics in the presence of impaired liver function. To study this we examined the effects of three models of experimental liver dysfunction and one of cytochrome P-450 inhibition on colchicine elimination in the rat. The models of experimental liver dysfunction included bile duct ligation (with sham-operated controls), alpha-naphthylisothiocyanate-induced intrahepatic cholestasis and galactosamine-induced diffuse hepatocellular necrosis. The control group had a colchicine clearance of 77.33 ml/min.kg +/- 8.27 ml/min.kg, a half-life of 16.68 min +/- 0.97 min and a volume of distribution of 1.84 L/kg +/- 0.15 L/kg. Cimetidine administration, 120 mg/kg intraperitoneally 15 min before colchicine administration, caused clearance to decrease by 32% (p less than 0.05) and half-life to increase by 38% (p less than 0.05). Volume of distribution did not change. At 48 hr after bile duct ligation, colchicine clearance decreased by 84% (p less than 0.05), terminal half-life increased to 513.7 min +/- 106.6 min (p less than 0.05) and volume of distribution increased by 175% (p less than 0.05). Colchicine pharmacokinetics in sham-operated rats were not statistically different from the above mentioned controls.(ABSTRACT TRUNCATED AT 250 WORDS)

1-Naphthylisothiocyanate↗
PubMed1990

Azidothymidine (zidovudine) transport by the human placenta.

The diagnosis of Acquired Immunodeficiency Syndrome (AIDS) is increasingly made in pregnant women, and the disease may be transmitted to the fetus. Azidothymidine (AZT, Zidovudine) is the one therapeutic agent of some promise in this condition. As there is no information on the transport of this drug by the human placenta, such studies were carried out using the single cotyledon placental perfusion system and human placental vesicles. AZT crossed the placenta readily and bidirectionally. The transfer rate was about 70% that of a freely diffusible reference marker, antipyrine, and was comparable in both directions. There was no evidence of active or carrier-mediated transport and no glucuronidated metabolites of the drug were identified in either maternal or fetal compartments. The authors believe that the drug crosses the placenta by diffusion, consistent with its lipophilicity and transport into various blood cells.

Antipyrine↗
PubMed1990

Thiamine-transfer by human placenta: normal transport and effects of ethanol.

Transport of "physiologic" concentrations of thiamine by the normal, term human placenta was studied by using the perfused cotyledon technique. Thiamine, 50 nmol/L, crossed from the maternal to fetal compartment at a rate somewhat below that of antipyrine, a freely diffusible marker drug. The transport was saturable and inhibited by structural analogues of thiamine, implying participation of carriers. Thiamine accumulated in the fetal compartment against a concentration gradient, suggesting active transport. Consistent with this, transfer of thiamine from the fetal to maternal compartment was significantly lower than in the opposite direction. The vitamin was concentrated in the placenta when compared with maternal and fetal levels. There was no evidence of phosphorylation of thiamine during its transfer. Exposure of the placenta to ethanol, 400 mg/dl, for up to 4 hours did not alter maternal-to-fetal transfer of the vitamin.

Antipyrine↗
PubMed1989

A model of cytochrome P-450-centered hepatic dysfunction in drug metabolism induced by cobalt-protoporphyrin administration.

Cobalt-protoporphyrin treatment disrupts cytochrome P-450-centered drug metabolism and is known to decrease significantly the cytochrome P-450 content of the liver. This study assesses further the correlations between biochemical and functional changes induced by Co-protoporphyrin. Specifically, it confirmed the fall in cytochrome P-450 levels in liver and demonstrated that both NADPH-cytochrome P-450 reductase and NADH-cytochrome b5 reductase activities decreased in a dose-dependent manner, albeit to a lesser degree, upon Co-protoporphyrin administration. Furthermore, plasma clearance of the marker drug aminopyrine fell off abruptly with a minimal decrease in cytochrome P-450 content, and then monotonically with its further depletion. Both aminopyrine and caffeine demethylation, as measured by the amount of radiolabeled CO2 exhaled, also decreased with diminishing cytochrome P-450 content. With aminopyrine the decrease was abrupt but with caffeine biphasic, consistent with preferential isozyme depletion. The drop in oxidative drug metabolism measured by these two in vivo techniques occurred in the absence of organellar damage to hepatocytes, as observed by electron microscopy. In vitro studies of aminopyrine metabolism in microsomes prepared from rats with and without Co-protoporphyrin injection proved to be consistent with the in vivo studies. Moreover aminopyrine Vmax decreased and Km increased with decreasing cytochrome P-450 content, suggesting preferential isozyme depletion. Furthermore, the changes in aminopyrine intrinsic clearance predicted by the in vitro Vmax and Km values agreed with those measured by in vivo plasma clearance. Taken together, these data suggest that Co-protoporphyrin treatment can be used to produce a model of altered cytochrome P-450-centered drug metabolism, as measured consistently by several techniques. However, this model appears to be more complex than one involving nonspecific depletion of cytochrome P-450 alone, and may be influenced also by concomitant changes in the electron transport chain or other aspects of hepatic metabolism.

Aminopyrine↗
PubMed1989

Ethanol effects on active Na+ and K+ transport in cultured fetal rat hepatocytes.

To define further the influence of ethanol on membranes, its effects on Na+ pump function were studied in monolayer cultures of fetal rat hepatocytes. The effects of ethanol (2 and 4 mg/ml) on total K+ influx, ouabain-sensitive K+ influx, Na+ pump density (from specific [3H]ouabain binding), pump turnover rates and intracellular Na+ were measured following exposure of the cells to ethanol for 1-24 hr. In parallel studies, the effects of ethanol (2 mg/ml) on cell water content and membrane fluidity were measured. Ethanol had no immediate effect on K+ influx, but after 1 hr ethanol in concentrations of 2 and 4 mg/ml decreased the total K+ influx (mumol/10(11) cells/sec) from a control of 8.5 +/- 0.64 to 4.46 +/- 0.50 and 4.09 +/- 0.26 respectively (N = 6 for each experiment; P less than 0.001). This represented the maximum effect of ethanol since after 6 and 24 hr of ethanol treatment the K+ influx had increased towards control levels but remained significantly (P less than 0.01 for 2 mg/ml and P less than 0.001 for 4 mg/ml) below that in control cells even at 24 hr. The decrease in K+ influx reflected a decrease in mean ouabain-sensitive K+ influx from a control of 5.87 to 3.24 and 2.70 (mumol/10(11) cells/sec) after a 1-hr treatment with 2 and 4 mg ethanol/ml medium respectively. Ethanol (2 mg/ml) treatment for 1-hr decreased Na+ pump density (x 10(5) molecules ouabain per cell) from a control of 2.80 +/- 0.30 to 1.70 +/- 0.11 (P less than 0.001). At 6 and 24 hr [3H]ouabain binding showed a pattern similar to that seen with the K+ influx, tending to return to pretreatment levels. There was no change in individual pump turnover rates in the presence of ethanol. Following exposure to ethanol, cellular Na+ content steadily increased over the first 6 hr and then returned to control levels. When corrected for parallel changes in cell volume, however, intracellular Na+ concentration increased by 17% (P less than 0.01) after 1 hr and thereafter remained at this higher level throughout the 24-hr period. Measurements of membrane fluidity showed that it was increased markedly by ethanol at a concentration of 2 mg/ml and that the effect bore a close temporal relationship to the changes in active K+ influx and Na+ pump density. We conclude that ethanol has a depressant effect on hepatic Na+ pump function, resulting in an increase in intracellular Na+ and an eventual gain in cell water.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1989

Effects of liver disease on the disposition of ciramadol in humans.

To determine the effects of liver disease on the disposition of ciramadol, an analgesic that undergoes ether glucuronidation, we studied its plasma pharmacokinetics in 10 patients with stable cirrhosis, 8 with acute viral hepatitis, and 16 age-matched healthy controls. Renal excretion of the glucuronides was also determined. In healthy controls given a single intravenous dose of the drug the t 1/2 was 3.4 +/- 0.3 hrs and the systemic clearance was 668 +/- 109 ml/min of which renal clearance was 320 +/- 73 ml/min and non-renal clearance 349 +/- 74 ml/min. The corresponding values after an oral dose were similar. Renal clearance was related directly to the estimated creatinine clearance. Moreover, the renal clearance of ciramadol exceeded creatinine clearance, suggesting that the drug was excreted not only by glomerular filtration but also by tubular secretion. The systemic clearance of intravenous ciramadol was diminished by 40% in cirrhosis, P less than 0.05, due to a reduction in renal clearance, while non-renal clearance remained normal. Renal clearance of the inactive glucuronides, on the other hand, was not affected. In patients with acute viral hepatitis, systemic clearance was unchanged, but renal clearance of ciramadol tended to increase during the acute phase of the disease and to return toward normal after recovery. Renal excretion of the inactive glucuronides was decreased by 48% (P less than .05). These findings suggest that the non-renal ether glucuronidation of ciramadol remains intact in patients with stable cirrhosis or acute viral hepatitis. However, the renal clearance of the drug may be impaired in cirrhosis, but tends to be enhanced in acute hepatitis.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

Effect of ethanol on human placental transport of model amino acids and glucose.

Prior studies in rodents, sheep, and subhuman primates have shown that ethanol, especially after chronic exposure, inhibits the transport of amino acids by the placenta. A small decrease in glucose transport by rat placenta chronically exposed to ethanol has also been noted. With human placental slices, however, only pharmacological (high) concentrations of ethanol impaired uptake of amino acids, and there are no data on glucose transport. In the present study, the effect of brief exposure to ethanol on human placental transport of model amino acids and glucose was studied by two techniques not previously jointly employed for this--the perfused human placental cotyledon and human placental vesicle systems. The nonmetabolizable amino acids, alpha-aminoisobutyric (AIB) acid and cycloleucine (CLEU), as well as D-glucose, and nonmetabolized glucose (3-O-methyl-D-glucose), were used as probes. AIB and CLEU are transferred normally by active transport and D-glucose by facilitated transport from maternal to fetal compartments. The perfused placental system was exposed to ethanol (300-500 mg%) for 2-4 hr and the vesicles to 200-400 mg% ethanol for times varying from 10 min to 48 hr. There was no impairment of AIB, D-glucose, or 3-O-methyl-D-glucose transfer by ethanol using these techniques. Normally, about 60% of AIB transport by human placenta is sodium dependent. This component (using the vesicle system) was also not impaired by ethanol. Ethanol caused a very small decrease of CLEU clearance by the perfused human placenta (p = 0.05) but not using vesicles.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

Impaired hepatic elimination of paranitrophenol and its metabolites in the rat following chronic ethanol pretreatment.

Chronic ethanol feeding has been shown to enhance hepatic microsomal drug oxidation in humans and in laboratory animals. However, the effects of chronic ethanol administration on drug conjugation are less conclusive. We have studied the effects of chronic ethanol feeding on (a) the conjugation and elimination of p-nitrophenol (PNP) by the isolated perfused rat liver, (b) the formation of PNP glucuronide by hepatic microsomal PNP-glucuronyltransferase in vitro and (c) the hepatic content of UDP-glucuronic acid (UDPGA). PNP elimination from the isolated perfused rat liver was best described as a combination of parallel saturable and first-order processes. Ethanol pretreatment did not influence the former but resulted in a 48% reduction in the rate of elimination by the latter. This was associated with a significant reduction in recovery of PNP-glucuronide from bile, but no change in concentrations of PNP glucuronide or sulfate in perfusate. Michaelis constants and Vmax for PNP-glucuronyltransferase in native and solubilized microsomes and UDPGA concentrations in liver were not influenced by ethanol pretreatment. These results suggest that chronic ethanol treatment reduces PNP elimination in the intact liver primarily via a reduction in the biliary excretion of PNP glucuronide without altering glucuronidation per se.

Animals↗
PubMed1989

Ethanol stimulates leucine uptake by rat fetal hepatocytes via trans-stimulation.

Prior studies showed that exposure of cultured rat fetal hepatocytes to ethanol increased sodium-independent transport of alpha-amino-isobutyric acid and cycloleucine. Using leucine (Leu) as a probe, we now show that this is a reflection of trans-stimulation of system L inward flux. Transport of Leu was entirely sodium independent and beta-2-aminobicyclo(2,2,1)-heptane-2-carboxylic acid inhibitable. Uptake kinetics indicated two components, likely systems L1 and L2 reported for the adult hepatocyte. The low-affinity Km was in the 0.5 mM range, whereas the high-affinity Km was 2% of that value. Under optimal growth conditions, approximately 65% of the Leu was transported by the latter system. Strong bidirectional exchange was shown with Leu loading, stimulating initial Leu uptake by 66%. Externally directed transport was enhanced 2.9 times against 5 x 10(-3) M Leu vs. no external Leu. A 24-h exposure to ethanol (2 mg/ml) increased Leu uptake by up to 100%, an effect that could be mimicked by arrested cell replication. Both enhanced rates could be reversed by amino acid depletion, reflecting intracellular amino accrual that induced trans-stimulation of Leu uptake. Enhanced uptake was also reproduced in replicating cells by loading with increasing concentrations of Leu.

Animals↗