IMPROVED ASSAY OF 7-ETHOXYCOUMARIN O-DEETHYLASE ACTIVITY - INDUCTION OF HEPATIC ENZYME-ACTIVITY IN C57BL-6J AND DBA-2J MICE BY PHENOBARBITAL, 3-METHYLCHOLANTHRENE AND 2,3,7,8-TETRACHLORODIBENZO-PARA-DIOXIN

Abstract

An improved in vitro fluorometric assay of the O-deethylation of 7-ethoxycoumarin which is at least 10 .times. more sensitive than existing methods is described. Nearly quantitative recovery of the product which is essentially free of fluorescent impurities is obtained by a simple 2-step extraction procedure. In C57BL/6J mice O-deethylating activity was induced 3-fold by 3-methylcholan threne and 7-fold by phenobarbital. Administration of phenobarbital resulted in a 10-fold stimulation of enzyme activity in DBA/2J mice. At least 2 and possibly more components are involved in the metabolism of 7-ethoxycoumarin. Differential stimulation of the maximal activities associated with these components was observed after the administration of phenobarbital, 3-methylcholanthrene or 2,3,7,8-tetrachlorodibenzo-p-dioxin. The ED50 [median effective dose] values for the induction by 2,3,7,8-tetrachlorodibenzo-p-dioxin of 7-ethoxycoumarin O-deethylase and aryl hydrocarbon hydroxylase activities in C57BL/6J mice were almost identical and approximately 10-fold less than in DBA/2J mice similarly treated.