Effect of chloroquine and phenobarbital on morphine glucuronidation and biliary excretion in the rat☆
Abstract
The relationship between morphine glucuronidation and biliary excretion was studied in rats pretreated with saline (control), chloroquine (CQ) or phenobarbital (PB) by determining the conversion of morphine to morphine-3-glucuronide (MG) in vitro and the biliary excretion of intravenously administered morphine and MG in vivo. For the biliary excretion studies. 14C-morphine or 14C-MG was administered intravenously and excretion measured in anesthetized renal-ligated rats in which the common bile ducts were cannulated. The effect of PB treatment on the biliary excretion of morphine and MG was complex and it was found that: (1) PB pretretment did not alter the proportions of morphine and MG in bile; (2) the rate of biliary excretion of morphine (as MG) was decreased in PB-pretreated rats even though MG formation was increased in vitro; (3) the plasma disappearance of 14C after 14C-morphine administration was also decreased by PB pretreatment; (4) the biliary excretion of administered MG was significantly decreased by PB pretreatment; and (5) the 14C plasma disappearance after 14C-MG administration was not changed by PB pretreatment. Several interpretations can be derived from these results. One possibility is that MG formation is not a rate-limiting step in the biliary excretion of morphine. An alternate interpretation would be that PB pretreatment may have an inhibitory effect on the biliary excretion of morphine and MG that is unrelated to metabolism. Chloroquine pretreatment produced only a slight effect on the biliary excretion of morphine and no effect on the biliary excretion of administered MG. Using studies in vitro, we could not demonstrate that CQ induced an increase in MG formation.
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Uncertainty factors for chemical risk assessment: Interspecies differences in glucuronidation
2001, Food and Chemical ToxicologyFor the risk assessment of effects other than cancer, a safe daily intake in humans is generally derived from a surrogate threshold dose (e.g. NOAEL) in an animal species to which an uncertainty factor of 100 is usually applied. This 100-fold is to allow for possible interspecies (10-fold) and interindividual (10-fold) differences in response to a toxicant, and incorporates toxicodynamic and toxicokinetic aspects of variability. The current study determined the magnitude of the interspecies differences in the internal dose of compounds for which glucuronidation is the major pathway of metabolism in either humans or in the test species. The results showed that there are major interspecies differences in the nature of the biological processes which influence the internal dose, including the route of metabolism, the extent of presystemic metabolism and enterohepatic recirculation. The work presented does not support the refinement of the interspecies toxicokinetic default to species- and pathway-specific values, but demonstrates the necessity for risk assessments to be carried out using quantitative chemical-specific data which define the fundamental processes which will influence the internal dose of a chemical (toxicokinetics), or the interaction of toxicant with its target site (toxicodynamics).
Previous work in this laboratory has suggested that the nonlinear disposition of valproic acid (VPA) in the rat may be due to nonlinear distribution of VPA into the liver. The present study was undertaken to elucidate further the hepatobiliary disposition of VPA. VPA (0.1-2 mmol/L) was incubated with isolated rat hepatocytes in vitro. Uptake of [3H]-VPA was linear from 10 to 50 seconds, with minimal (<7 percent) biotransformation. The initial velocity of VPA uptake varied in proportion with the extracellular concentration and was temperature independent, suggesting that VPA traverses the hepatocyte membrane predominantly by passive diffusion. In separate studies, the hepatobiliary disposition of VPA (20mg) was examined in the isolated perfused rat liver (IPL). A pharmacokinetic model was developed to describe the influence of phenobarbital on the hepatobiliary disposition of VPA and valproate glucuronide (V-G) in the IPL; all processes governing VPA and V-G disposition appeared to be linear. Acute administration of phenobarbital to the liver (1.12 mg) decreased the rate constant for canalicular egress of V-G (0.0489 +/- 0.0266 vs. 0.164 +/- 0.075 min-1). In vivo pretreatment with phenobarbital (75 mg/kg/d x 5 d) before liver isolation decreased the biliary excretion of both VPA (1.06E-04 +/- 0.27E-04 vs. 2.76E-04 +/- 0.45E-04 min-1) and V-G (5.63E- 03 +/- 1.98E-03 vs. 1.74E-02 +/- 0.5E-02 min-1), and increased the apparent volume of distribution of VPA (84.6 +/- 2.2 vs. 72.3 +/- 2.1 mL). In vivo phenobarbital pretreatment a changed V-G excretion from a formation to an elimination rate-limited process. These results are consistent with phenobarbital-associated impairment of canalicular egress of some organic anions. This work further supports the utility of pharmacokinetic modeling in: (1) determining the rate-limiting steps in hepatobiliary drug disposition and (2) identifying sites of drug interactions within the hepatobiliary system that may not be evident based on conventional mass-balance analysis. (Hepatology 1996 Apr;23(4):771-80)
Enterohepatic recirculation and renal metabolism of morphine in the rat
1991, Journal of Pharmaceutical SciencesMorphine (2.5 mg/kg) was administered iv to intact (I), bile duct-cannulated (BC), and bile duct-cannulated–renal-ligated (BC–RL) rats (n = 4 per group) to investigate the extent of enterohepatic recirculation and renal metabolism of the drug. A decrease in the serum area under the concentration–time curve (AUC) was observed for the BC in comparison with I rats. From these AUC values, it was determined that ~16% of the administered dose was subject to enterohepatic recirculation. In addition, a statistically significant (p < 0.05) decrease in the systemic clearance of morphine was observed in the BC–RL rats compared with the BC animals (55.2 ± 17.2 versus 31.4 ± 8.5 mL/min/kg). This decrement in systemic clearance appeared to be the result of a significant decrease in the formation clearance of morphine glucuronide after ligation of the renal pedicles (23.2 ± 4.8 versus 10.9 ± 5.0 mL/min/kg). Renal metabolic clearance was calculated as 15.7 mL/min/kg, accounting for 28.5% of the systemic clearance of morphine. Hepatic clearance (31.4 ± 8.5 mL/min/kg) accounted for 56.8% of total systemic clearance.
Demonstration of cell sidedness in hepatic transfer of morphine and morphine glucuronide in the rat
1986, Biochemical PharmacologyThe purpose of this study was to demonstrate hepatic cell sidedness for the transfer of [14Cjmorphine and [14C]morphine glucuronide. A tracer dose of [14C]morphine was administered by segmented retrograde intrabiliary injection into the bile duct cannula of the urethane-anesthetized rat or the in situ isolated perfused liver preparation. The bile from the first, and the single pass perfusate from the second preparation, respectively, were analyzed for the radioactive components. Various doses of morphine were given intraportally in these preparations 5 min before the [14C]rnorphine to influence the recovery of the radioactive components. As the dose of morphine increased, the recovery in bile of [14C]morphine glucuronide decreased while [14C]morphine remained unchanged. In the perfusate, the morphine loading increased the recovery of [14C]morphine, but the [14C]Cimorphine glucuronide content was unchanged. These sets of results indicated that morphine loading inhibited the formation of morphine glucuronide by isotope dilution, which should have led to an increase in [14C]morphine in the cell. Because of the presence of cell sidedness, the increased intracellular [14C]morphine was directed toward the perfusate and not toward the bile. The decrease in [14C]morphine glucuronide synthesis was manifested by a decrease in its excretion into bile, but not into perfusate. Further demonstration of cell sidedness was obtained by manipulation of these systems by chlordecone and trans-stilbene oxide pretreatment of the rats. The directionality of flow of [14C]morphine and [14C]morphine glucuronide out of the liver emanates from liver cell sidedness.
Mirex-induced suppression of biliary excretion of polychlorinated biphenyl compounds
1976, Toxicology and Applied PharmacologyIsolated perfused rat liver preparations were utilized to study the drug-induced modification of biliary excretion of [14C]4-chlorobiphenyl (1-CB) and [14C]2,4,5-2′,4′,5′-hexachlorobiphenyl (6-CB) and their metabolites. The effect of pretreatment of rats with mirex was compared with that of phenobarbital (PB) and 6-CB by measuring the biliary excretion of 1-CB and the pharmacokinetics of 1-CB and its metabolites in the perfusate of liver preparations obtained from control and treated rats. The biliary excretion of 1-CB metabolites by mirex-pretreated livers was suppressed by 92% of that in control livers. The rate of metabolism of 1-CB by mirexpretreated livers was slightly decreased. However, the suppression of biliary excretion of 1-CB metabolites does not appear to be related either to decreased rate of metabolism or to the rate of bile flow. These conclusions are borne out from the following two observations: first, the metabolites of 1-CB accumulate at increasing concentrations in the perfusate of mirexpretreated livers; secondly, mirex-pretreated livers had elevated bile flows. Biliary excretion of exogenously added metabolites of 1-CB by mirextreated livers was suppressed by 85% of that of control livers. PB and 6-CB pretreatment caused a statistically significant increase in the biliary excretion of 1-CB metabolites. This was accompanied by a slight but statistically nonsignificant increase in the rate of bile flow. Biliary excretion of 6-CB was completely suppressed by mirex pretreatment and was unaffected by PB. These results indicate that while PB-induced modification of biliary excretion of PCBs may be associated with their metabolism, mirex-induced suppression is associated with the transport of otherwise readily excretable metabolites from the hepatocytes into the bile canaliculi.
Effect of phenobarbital pretreatment on the metabolism and biliary excretion of methadone
1975, Biochemical PharmacologyThe effect of phenobarbital (PB) pretreatment on the biliary excretion of methadone in rats was studied. Possible mechanisms by which PB pretreatment altered the biliary excretion of methadone were considered and studies in vitro on the metabolism of methadone were correlated with findings in vivo. For the biliary excretion studies, 14C-methadone was administered intravenously and biliary excretion measured in anesthetized renal-ligated rats in which the common bile duct was cannulated. PB pretreatment increased the biliary excretion of 14C after 14C-methadone administration. The different metabolites of methadone formed in vivo and excreted into bile were separated by thin-layer chromatography and quantitated. The biliary excretion of the metabolite which results from N-demethylation and cyclization of methadone was not altered by PB pretreatment. However, the biliary excretion of metabolites which result from further N-demethylation, hydroxylation and glucuronidation was increased by PB pretreatment. Several determinants of biliary excretion (i.e. bile flow, hepatic blood flow and metabolism). which are enhanced by PB pretreatment, could cause the observed increase in the biliary excretion of methadone. Of these possibilities, we feel the data best support the suggestion that enhancement of methadone metabolism by PB pretreatment is responsible for the increased biliary excretion of methadone in PB-pretreated rats. Furthermore, metabolism studies in vitro, using microsomes from PB-treated rats, support the suggestion that PB pretreatment enhances the metabolism of methadone in vivo.
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Preliminary results were presented at the Fifty-seventh Annual Meeting of the Federation of American Societies for Experimental Biology, Atlantic City, New Jersey, 15 20 April. 1973.
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Supported by United States Public Health Service Grant GM 16503.