Further evidence in support of a short-loop feedback action of estrogen on ovarian androgen production

We have demonstrated previously an ability of estrogen to inhibit ovarian androgen production. We report here further evidence in support of this intraovarian short-loop feedback mechanism. Thecal cells from ovarian follicles of estradiol-17β (E)-treated rats demonstrated an enhanced capability of producing progesterone in response to LH $\text{in vitro}$. In contrast, testosterone production by the same thecal preparations was markedly inhibited by pretreatment with E, suggesting a selective inhibitory action of E at the level of the androgen-producing cells in the ovarian follicle. In a somewhat contrasting experiment in hypophysectomized rats, while simultaneous administration of purified follicle-stimulating hormone (FSH) antagonized an inhibitory action of E on ovarian progesterone production, treatment of the hypophysectomized rats with either E alone or concomitantly with E plus FSH still attenuated ovarian testosterone production by these animals in response to acute LH stimulation. These results are consistent with a direct inhibitory action of estrogen at the level of the ovarian C_17α-hydroxylase /C_17,20-lyase enzyme system.