In studies on the molecular basis of hormone action during granulosa cell differentiation, emphasis was placed on the functions and mechanisms of action of growth factors and plasminogen activator. TGF-beta exerted bifunctional actions on the maturation of granulosa cells, and altered the simulation of cAMP formation, steroidogenesis, and LH receptor expression by FSH in a concentration-dependent manner. TGF-beta amplified gonadotropin responses in the presence of small amounts of FSH, but had less effect or even inhibited FSH actio when FSH levels were elevated. The inhibitory effects of TGF-beta were observed only in the presence of insulin, suggesting that the total complement of hormones and growth factors within ovarian follicles determines the eventual development of granulosa cells. TGF-beta also modified EGF action during granulosa cell maturation through direct effects on EGF receptors. FSH increased EGF receptors during granulosa cell differentiation through elevations in cAMP levels. TGF-beta augmented the effects of FSH on EGF receptors, as well as increasing these binding sites in the absence of gonadotropin. The enhancement of EGF receptors by TGF-beta resulted in a parallel rise in the inhibitory effects of EGF on FSH-induced cAMP production and LH receptor formation. In studies designed to characterize specific proteins induced by FSH in granulosa cells, gonadotropin was shown to stimulate the production of a cell-surface tissue- type plasminogen activator, while both FSH-treated and control cells synthesize intracellular urokinase-plasminogen activators. Hormonal regulation of the production and activities of these enzymes may allow the expression of specific differentiated function of granulosa cells. In cultured human syncytiotrophablasts from term placentae, the anti-progestin RD486 was shown to inhibit production of hCG, hPL, and progesterone. Also, arachidonic acid was found to be an exceptionally potent stimulus of hCG and hPL production, with effets in the nanomolar concentration range. It appears likely that placental hormone secretion, like pituitary hormone release, is influenced by lipoxygenase products of arachidonic acid.
