Effect of acute and repeated selenium treatment on hepatic monooxygenase enzyme activity in male rats.

The effect of sodium selenite administered acutely or repeatedly on the biochemical components of the hepatic microsomal monooxygenase enzyme system was examined in male rats. 72 h following acute administration of selenium (2.4 mg Se/kg, i.p.), there was a significant decrease in ethylmorphine-N-demethylase activity and cytochrome P-450 levels but no change in aniline hydroxylase or NADPH cytochrome c reductase activity. Following repeated administration of selenite in the drinking water (1, 2, or 4 ppm Se) for 30 days, there was no alteration in any of the parameters measured. Following the in vitro additions of selenite to microsomes obtained from untreated rats, ethylmorphine-N-demethylase and aniline hydroxylase activities were inhibited at selenium concentrations of 10(-4) M or greater, but the inhibition achieved was less than 50%. No alterations in cytochrome P-450 levels were observed. These results indicate that selenium is a rather weak, indirect, and substrate-specific inhibitor of the hepatic monooxygenase enzyme system.