Activin inhibition of estradiol and progesterone production in porcine granulosa cells.

Two studies evaluated the influence of activin on steroidogenesis in cultured porcine granulosa cells obtained at various stages of differentiation. In granulosa cells isolated from 1- to 3-mm follicles, obtained at random stages of the estrous cycle, treatment with activin or transforming growth factor beta (TGF beta) decreased progesterone production during the first 48 h of culture, but neither had an effect on estradiol production. One-half of these cells received FSH treatment at 48 h, and at 96 and 144 h of culture FSH increased estradiol and progesterone production. Activin or TGF beta reduced, in a dose-dependent manner, both basal and FSH-stimulated production of both steroids. In the second study, granulosa cells were obtained during follicular growth associated with weaning and were separated into two subpopulations (weakly associated [WA] and tightly bound [TB]). Estradiol production in culture increased with time after weaning. Tightly bound cells produced more estradiol than WA cells and maintained FSH-stimulated estradiol production, whereas production of progesterone increased in both cell types after treatment with FSH. Activin depressed FSH-stimulated estradiol production in TB cells and depressed FSH-stimulated progesterone production in both cell types. These results clearly indicate that activin depresses in vitro steroidogenesis by granulosa cells from antral, porcine follicles; thus, activin may participate in atresia of antral follicles of this species.