Abstract
The mammalian ovarian cycle is a strictly regulated process that is dependent on the intimate interactions among the 3 cell types in the follicle — theca, granulosa, and oocyte. The cycle has been shown to be controlled by gonadotropins as well as locally produced peptide factors. In this study, an in vitro culture system was used to study the roles of 2 locally produced ovarian peptide factors, transforming growth factor- β 1 (TGF- β 1) and activin-A, on porcine granulosa cell steroidogenesis. Gonadotropin stimulated cultured porcine granulosa cells (from medium-sized follicles) were pretreated with 100 ng/ml follicle-stimulating hormone (FSH) for 48 h and then treated with 1 ng/ml TGF- β 1, 100 ng/ml activin-A, TGF- β 1 plus activin-A, or received no treatment (control) for 48 h, From our previous studies, the concentrations of the 2 growth factors were determined to produce maximal antisteroidogenic effects in porcine granulosa cells. Progesterone (P 4) production, estradiol-17β (E 2) production, and aromatase activity for gonadotropin-stimulated porcine granulosa cells treated with TGF- β 1, activin-A, and TGF- β 1 plus activin-A were significantly (P < 0.05) reduced fromthat of the control. The same procedures were conducted on basal steroidogenesis studies in which no pretreatment with FSH was performed. Both P 4 and E 2 production and aromatase activity for porcine granulosa cells treated with TGF- β 1, activin-A and TGF- β 1 plus activin-A were significantly (P < 0.05) inhibited compared with the control. Our results indicate that both TGF- β 1 and activin-A can inhibit FSH-stimulated and basal steroidogeneses in porcine granulosa cells and, thus, may act as local atretic factors during follicular development. When the 2 growth factors were given in combination at concentrations that would produce maximal steroidogenic inhibition, they were not able to produce a synergistic effect. These results are consistent with the current theory that TGF- β 1 and activin-A may act via the same messenger system, a serine-threonine kinase.
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