| Abstract: | The induction of luteinizing hormone (LH) receptors was studied in granulosa cells prepared from the ovaries of hypophysectomized diethylstilbestrol-treated immature rats. Incubation of granulosa cells for 48 h with increasing concentrations of follicle-stimulating hormone (FSH) or choleragen caused parallel rises in cAMP levels and LH receptors. These observations, with the finding that 8-Bromo-cAMP also induced LH receptor formation, indicate that hormonal stimulation of LH binding sites is mediated by cAMP. Peptide hormones that inhibited FSH-stimulated cAMP production, such as epidermal growth factor (EGF) and a gonadotropin-releasing hormone agonist (GnRHa), also prevented LH receptor formation. GnRHa and EGF had negligible effects on FSH-stimulated cAMP production from 0 to 24 h of culture, but reduced cAMP accumulation by 80% and 90%, respectively, from 24 to 48 h when the majority of LH receptors appeared. FSH-sensitive adenylate cyclase activity, as measured by the conversion of (3H)-ATP to (3H)-cAMP, was inhibited by GnRHa and EGF at 48 h of culture. EGF and GnRHa also reversed the inhibition of ectophosphodiesterase activity caused by FSH in granulosa cells between 48 and 72 h of culture. Both EGF and GnRHa inhibited induction of LH receptors by 8-Bromo-cAMP, suggesting that their effects are also on cAMP action. Addition of GnRHa, but not EGF, between 36 and 48 h of culture completely prevented further increases in LH receptors induced by 8-Bromo-cAMP, indicating that the inhibitory action of GnRHa can be initiated at later times during granulosa cell differentiation, whereas full expression of EGF action requires a longer period. These results demonstrate that EGF and GnRH inhibit FSH-induced LH receptor formation in the granulosa cell by reducing hormone-dependent cAMP production and also by impairing the ability of cAMP to stimulate LH receptor formation. |
