The effects of estradiol and progesterone on rat ovarian 17-hydroxylase and 3ß-hydroxysteroid dehydrogenase activities

Testosterone biosynthesis by Leydig cells can be modulated by estradiol. This modulation appears to occur at the 17-hydroxylase and 17,20-desmolase stage. In this study we have examined the effects of estradiol and progesterone on the activities of the 17-hydroxylase (17-OH) and 3ß-hydroxysteroid dehydrogenase (3ß-HSD) in rat ovarian tissue, to examine the hypothesis that estradiol may regulate these enzymes in the ovary as well as in the testis. Estradiol capsule implants produced a decrease in 17-OH activity (0.5 ± 0.05 vs. 2.1 ± 0.1 nmol/mg protein/min, mean ± SEM, p< 0.001), and an increase in 3ß-HSD activity (15.5 ± 0.9 vs 9.7 ± 0.7 nmol/mg protein/min p < 0.001). Progesterone injections produced a decrease in both 17-OH (0.9 ± 0.1 vs. 2.3 ± 0.2 p<0.005) and 3ß-HSD (2.5 ±.4 vs. 8.6 ± 0.5; p <0.005) activities. We conclude that estradiol decreases 17-OH activity in the ovary as it does in the testis. This, coupled with an increase in 3ß-HSD may explain the pre-ovulatory increase in progesterone seen in many species. Progesterone seems to decrease the steroidogenic activity of the ovarian tissue, perhaps offering an explanation for the gonadotropin resistance seen in corpus luteum bearing ovaries.