| Abstract: | Increasing doses of estradiol-17 beta added to in vitro incubations inhibited pregnenolone-induced germinal vesicle breakdown in Rana pipiens ovarian follicles. The inhibition was reversed with increasing concentrations or pregnenolone added to the medium. Because no evidence of estradiol-17 beta inhibition or interaction with progesterone-induced GVBD was observed, the effect of estradiol-17 beta on the conversion of 3H-pregnenolone to 3H-progesterone was investigated. Estradiol-17 beta in doses as low as 10(-7) M significantly inhibited the conversion of 3H-pregnenolone to 3H-progesterone in follicles incubated in vitro. It is suggested that estradiol-17 beta is a feedback inhibitor of 3 beta-hydroxysteroid dehydrogenase-isomerase, the enzyme complex that converts pregnenolone to progesterone, a necessary step in the initiation of GVBD. |
