Seasonal change and sex difference in drug-metabolizing activity in frog liver microsomes

The drug-metabolizing activities (aminopyrine N-demethylase and p-nitroanisole O-demethylase activities) have been measured at monthly intervals throughout the year in liver microsomes of male and female Japanese bullfrogs, Rana catesbeiana. The aminopyrine N-demethylase activity based on cytochrome P-450 of both sexes was significantly higher in May-July (spring-summer) than in August-October (summer-autumn). On the contrary, the p-nitroanisole O-demethylase activity based on cytochrome P-450 of males was significantly higher in July-October (summer-autumn) than in May-June (spring). However, there was no seasonal changes in the O-demethylase activity in females. There were significant differences between males and females in the N-demethylase activity in August-October and in the O-demethylase activity in May-June (or July-October).