EFFECTS OF ETHANOL ON ETHYLMORPHINE METABOLISM IN ISOLATED RAT HEPATOCYTES - CHARACTERIZATION BY MEANS OF A MULTICOMPARTMENTAL MODEL

Hepatic cytochrome P-450 enzymes mediate at least two important biotra nsformation pathways of codeine and ethylmorphine starting with either N-demethylation or O-dealkylation, producing polar metabolites which are then subsequently glucuronidated. The present study was designed t o characterise the acute effects of ethanol on the metabolism of ethyl morphine and to compare it with the effects on codeine in suspensions of freshly isolated rat hepatocytes. Isolated rat hepatocytes from mal e Wistar rats were prepared by a collagenase perfusion method. Ethylmo rphine, codeine and their metabolites were quantified by HPLC with UV detection. The total ethylmorphine elimination rate was reduced by 12% at 5 mM and 38% at 100 mM ethanol. The corresponding percentages for codeine were 16 and 43%. In the presence of ethanol the concentrations of several intermediate and end products of ethylmorphine and codeine changed markedly from the control situation. The experimental data we re applied to a mathematical compartmental linear model to estimate th e influence of ethanol on the separate reaction rates in the two main metabolic pathways. The ratios between reaction rate constants in the ethylmorphine experiments at 100 and 0 mM ethanol were 0.65 for ethylm orphine-->norethylmorphine, 0.63 for norethylmorphine-->normorphine, 0 .56 for ethylmorphine-->morphine, 0.49 for morphine-->normorphine, 0.3 1 for normorphine-->normorphine-3-glucuronide and 0.49 for morphine--> morphine-3-glucuronide. Almost similar effects of ethanol on codeine m etabolism were found. In additional experiments, norethylmorphine or n orcodeine (50 mu M) was incubated with 5 mM to 100 mM of ethanol and t he metabolism of both norethylmorphine and norcodeine was found to be inhibited by ethanol in a concentration-dependent manner. The glucuron idation of morphine and normorphine added in separate experiments was also inhibited by ethanol, from 22 to 36% for morphine-3-glucuronide a nd 30 to 60% for normorphine-3-glucuronide, respectively, in the prese nce of 5 mM to 100 mM of ethanol. It was concluded that all steps in t he metabolism of ethylmorphine (and codeine) leading to the end produc ts morphine-3-glucuronide and normorphine-3-glucuronide were inhibited by ethanol, and that the glucuronidation processes were the ones most affected by ethanol.