Sex differences in cytochrome P-450 and mixed-function oxygenase activity in gonadally mature trout

Levels of microsomal cytochrome P-450 and aminopyrine demethylase activity in liver and of cytochrome P-450 in kidney of gonadally mature rainbow and brook trout were markedly greater in males than in females. Similar differences appeared in hepatic microsomal NADH- but not in NADPH-cytochrome c reductase activity or cytochrome b₅ content. When normalized to cytochrome P-450 content, benzo[a]pyrene hydroxylase activity in both liver and kidney was greater in females. In liver, there was a pronounced sex difference in the response of this activity to 7,8-benzoflavone, suggesting cytochromes P-450 of different catalytic function. Electron paramagnetic resonance spectra of hepatic microsomal cytochromes P-450 in mature brook trout were not demonstrably different between males and females, and crystal field parameters indicate that axial ligands to the neme are the same in these as in other cytochromes P-450. Mixed-function oxygenase activities in liver of gonadally immature brook trout differed from those in mature fish, and there was no sex difference. The appearance of seasonally dependent sex differences suggests that fish may provide interesting models for studying regulation of sex-specific forms of cytochromes P-450.