[C-14] 7-ETHOXYCOUMARIN METABOLISM BY PRECISION-CUT RAT HEPATIC SLICES

The metabolism of [C-14]7-ethoxycoumarin ([C-14]7-EC) has been studied in rat liver slice cultures in vitro by using a direct radiometric hi gh-pressure liquid chromatography method. [C-14]7-EC was extensively b iotransformed in these incubations to 7-hydroxycoumarin (7-OHC), 7-hyd roxycoumarin glucuronide, and 7-hydroxycoumarin sulfate, as well as to a large number of previously unrecognized metabolites, the majority o f which are sulfate conjugates. The liver slice [C-14]7-EC metabolite profile was also very complex and seemed to be qualitatively similar t o the medium metabolite profile. Quantitative comparisons, however, de monstrated that there was approximately two to five times more 7-OHC i n the liver slice than in the medium, whereas 7-hydroxycoumarin sulfat e, the most abundant metabolite in the medium, was present only at low levels in the liver slice. These data demonstrate that 7-OHC levels a re considerably underestimated when only levels in the medium are cons idered. Total metabolite levels were approximately equal in the medium and liver slice after a 2-hr incubation, with considerably higher tot al metabolite levels present in the medium at the end of the incubatio n period (8 hr). Additional studies are needed to identify the structu res of the previously unrecognized metabolites observed in this study and the enzymes responsible for their formation, as well as studies to define the metabolism of [C-14]7-EC in other in vitro models by using tissue from humans and other animal species.