Estrogen Augmentation of Gonadotropin-Stimulated Progestin Biosynthesis in Cultured Rat Granulosa Cells*

Abstract

The influence of estrogens on gonadotropinstimulated production of progesterone and 20α-hydroxypregn- 4-en-3-one (20α-OH-P) was examined in primary cultures of rat granulosa cells. Granulosa cells were cultured for 3 days with increasing concentrations of FSH in the presence or absence of either diethylstilbestrol (DES) or estradiol. FSH treatment increased progestin production in a dose-dependent manner, whereas treatment with estrogens alone were ineffective. In contrast, concomitant addition of either DES or estradiol augmented FSH-stimulated production of progesterone and 20α- OH-P. Increasing concentrations of estradiol (10^-10 – 10^-7 M) augmented the stimulatory effect of FSH (30 ng/ml) on progesterone production in a dose-dependent manner with ED₅₀ values of approximately 3 × 10^-9 M. The facilitatory action of estradiol was time-related, becoming significant after 36 h of treatment. Granulosa cells were also cultured for 2 days with FSH to induce functional LH receptors. The FSH-primed cells were treated for an additional 3 days with increasing concentrations of LH (0.3– 30 ng/ml) in the absence or presence of DES (10^-7 M). LH stimulated progesterone and 20α-OH-P production in a dosedependent manner, whereas concomitant addition of DES further enhanced LH-induced progestin biosynthesis. (Bu)₂cAMP also increased progesterone and 20α-OH-P production by the granulosa cells; however, concurrent addition of DES did not augment the actions of (Bu)₂cAMP. The effect of estrogens on gonadotropin-stimulated cAMP accumulation was also examined. FSH treatment dose-dependently increased cAMP accumulation, whereas concomitant treatment with estradiol further increased the FSH action. Similarly, LH treatment also stimulated cAMP accumulation in FSH-primed cells, whereas concurrent addition of DES further augmented LH action. Thus, the stimulatory effect of estrogens upon gonadotropin-stimulated progestin production may be related to the augmentation of cAMP biosynthesis. The present observations suggest that intraovarian estrogens may act locally to enhance the sensitivity of granulosa cells to FSH and LH, thereby increasing the biosynthesis of progestins and cAMP by the granulosa cells.