On the presence and regulation of 3 alpha-hydroxysteroid dehydrogenase in the adult rat ovary.

The presence of 3 alpha-hydroxysteroid dehydrogenase activity in adult rat ovaries was assessed by direct measurement of the conversion of dihydrotestosterone to 5 alpha-androstan-3 alpha, 17 beta-diol (3 alpha-diol). This enzyme was indeed found in this tissue with a high specific activity (414--560 nmol of 3 alpha-diol formed/h/mg protein) when compared to other hormone-dependent tissues. During the 4-day rat estrous cycle, the enzymatic activity was found to fluctuate by approximately 30% with the peak of activity at proestrus and the nadir at estrus. Further evidence for the hormonal regulation of this enzymatic activity was obtained with hypophysectomy and hormone replacement studies. Hypophysectomy resulted in a nearly 50% decrease when activity is expressed per ovary but this treatment had no significant effect on the specific activity (per mg ovary or per mg protein) of the enzyme. Hormone replacement, via polydimethylsiloxane capsules, with estradiol-17 beta resulted in a doubling of ovarian 3 alpha-HSD activity per mg protein but no significant change on a per ovary basis while replacement with testosterone caused a major decrease in activity to 15--30% (depending on the mode by which enzyme activity is expressed) of control hypophysectomized animals. These data thus indicate that this enzyme activity is present in the ovary and that it is regulated by gonadotrophins or gonadotrophin-induced steroids. The potential significance of these observations on follicular development and atresia is discussed.