Transforming growth factor beta enhances basal and FSH-stimulated inhibin production by rat granulosa cells in vitro

Transforming growth factor beta (TGF beta) caused a dose-dependent increase in both basal and follicle-stimulating hormone (FSH)-stimulated inhibin production by rat granulosa cells in culture. The TGF beta dose-response curve in the absence of FSH was approximately parallel to that in the presence of either a minimally effective dose (1 ng/ml) or a maximally effective dose (30 ng/ml) of FSH, suggesting an additive effect of these two agents on inhibin production. There was also a suggestion of an increased sensitivity of granulosa cell inhibin production to FSH when the cells were coincubated with TGF beta. The time course study showed that similar to FSH, the stimulatory effect of TGF beta on basal and FSH-stimulated inhibin production was evident on day 1 and was maximal by day 4. In addition, epidermal growth factor (EGF) reduced FSH-stimulated inhibin production with an ID50 value of 1.3 ng/ml. Coincubation of cells with EGF and 1 ng TGF beta/ml enhanced greatly the inhibitory action of EGF on FSH-induced inhibin production (ID50 less than 0.1 ng/ml). It is concluded that: (1) TGF beta directly stimulates inhibin production by rat granulosa cells and the combined effect with FSH was largely additive, (2) the inhibitory effect of EGF on FSH-induced inhibin production was enhanced by TGF beta, (3) individual members of the TGF beta/inhibin gene family regulate ovarian function, not only by direct action on follicle cells but also indirectly by influencing the production rate of other members of that family.