The influence of oestradiol on androgen- and oestrogen-dependent enzyme activities of hepatic steroid metabolism in rats.

Five sexually differentiated enzyme activities of hepatic steroid metabolism (cytoplasmic 17 beta-hydroxysteroid dehydrogenase, 5 beta-reductase; microsomal 3 alpha- and 3 beta-hydroxysteroid dehydrogenase and 5 alpha-reductase) were investigated in intact, gonadectomized and hypophysectomized rats after administration of a single dose of oestradiol valerate. Oestradiol administration caused a partial or complete feminization of these activities in intact male rats. The influence of oestradiol on these activities in gonadectomized rats was determined by the mode of sex hormone-dependent regulation of the individual activity: the most prominent effects were seen in the oestrogen-dependent activities (17 beta-hydroxysteroid dehydrogenase, 5 beta-reductase); no effect was seen in the completely androgen-dependent 3 alpha-hydroxysteroid dehydrogenase because gonadectomy alone was sufficient to cause complete feminization of the activity. Oestradiol administration had no effect on the activities of hypophysectomized rats. The fact that oestrogen administration to intact male rats caused greater changes than prepuberal gonadectomy demonstrates that oestrogen action is more than simple suppression of testicular function.