Initial characterization of the hepatic microsomal cytochrome P-450-system of the piked whale (Minke) Balaenoptera acutorostrata

Components of the microsomal cytochrome P-450- system were measured in liver samples from several female, one male and two foetal piked whales. In the same samples, four éytochrome P-450- dependent monooxygenase activities were assayed, protein pattern was determined by SDS-polyacrylamide gel e electrophoresis and the regiospecificity of phenanthrene metabolism in vitro was determined by gas chromatography/mass spectrometry. Foetal samples contained cytochrome P-450, cytochrome b 5 and NADPH-cytochrome P-450,reductase, but at lower levels than adults. Of the monooxygenase activities, only the O-deethylation reactions (7-EROD ∗ and 7-ECOD) could be detected in the foetuses. The turnover of 7-ethoxyresorufin was even higher than in most ofthe adult samples. In the adult samples, apparent differences could be observed in the parameters investigated between immature specimens of different sex and between immature and mature female whales. In vitro metabolism of phenanthrene showed a clear preference for attack at the 9,10-position by adult liver microsomes, where 10–35% appeared as the 1,2-dihydrodiol, with large individual variations. When metabolized by foetal liver microsomes, only 25–35% of total phenanthrene metabolites appeared as the 9,10-dihydrodiol, whereas 38–50% were the 1,2-dihydrodiol. Between 16 and 32% of the metabolites in all samples were phenols.