BIOTRANSFORMATION OF ROTENONE BY HEPATIC MICROSOMES FOLLOWING PRETREATMENT OF RAINBOW-TROUT WITH INDUCERS OF CYTOCHROME-P450

The in vitro biotransformation of rotenone by hepatic microsomes from rainbow trout (Oncorhynchus mykiss) was investigated following pretreatment of animals with β-naphthoflavone (BNF), phenobarbital, piperonyl butoxide (PBO), and rotenone. Using microsomes from control (untreated) animals, three major and several minor metabolites of rotenone were observed in chromatograms of incubations. The major metabolites were determined by high-performance liquid chromatography and mass spectrometry to be rotenolone and 2 epimeric forms of 6′,7′-dihydro-6′,7′-dihydroxyrotenone (DDRN). Pretreatment of trout with rotenone or phenobarbital resulted in no significant changes in the activity of hepatic microsomes for rotenone metabolism, 7-ethoxyresorufin-O-deethylase (EROD) activity, or 7-ethoxycoumarin-O-deethylase (ECOD) activity. Pretreatment of trout with BNF or PBO resulted in significant elevations in the activity of EROD and ECOD in hepatic microsomes. Pretreatment with PBO, but not BNF, significantly reduced the rate of oxidation of rotenone in hepatic microsomes. The in vitro oxidation of rotenone to rotenolone by hepatic microsomes was inhibited by pretreatment of trout with PBO at 4 and 0.01 ppm, but only pretreatment with 4 ppm PBO was able to inhibit the oxidation of rotenone to DDRN. The data indicate that PBO and BNF induction of hepatic microsomal monooxygenases may qualitatively differ from each other, that rotenone may be metabolized by more than one cytochrome P450 isozyme, and that PBO may selectively and dose-dependently inhibit specific cytochrome P450 isozymes that are involved in rotenone oxidation, and that none of the treatments appeared to selectively increase the formation of any of the metabolites. © 1992.