Adenylate Cyclase of Porcine Granulosa Cells: Differential Response to Gonadotropins during Follicle Maturation*

Abstract

The human FSH [follitropin] (hFSH)- and human LH [lutropin] (hLH)/hCG[human chorionic gonadotropin]-mediated adenylate cyclase activities of granulosa cells from small (1-2 mm), medium 3-5 mm) and large (6-12 mm) porcine ovarian follicles were studied. The adenylate cyclase of small follicle cells was highly sensitive to hFSH with an 8- to 13-fold increase over the basal activity, whereas hCG had little effect (only a 2-fold increase) on the enzyme activity. The stimulation by hFSH cannot be accounted for by hLH contamination, since hFSH had a larger stimulatory effect and a lower apparent concentration for half-maximal stimulation (apparent Km, 370 ng/ml) than that of hLH (apparent Km, 1700 ng/ml). The adenylate cyclase of granulosa cells became increasingly responsive to hCG and hLH as the follicles developed. hCG at the saturating concentration stimulated the enzyme activity with a 4-fold increase in medium follicle cells and with a 10- to 14-fold increase in large follicle cells without change in the apparent Km. hLH had a stimulatory effect similar to that of hCG. Adenylate cyclase lost its response to hFSH in large follicle cells. The apparent Km for hFSH (2000-2800 ng/ml) was considerably higher than the value for hLH (90-160 ng/ml). The adenylate cyclase activity observed in large follicle cells could be attributed to hLH contamination. The medium follicle cells appeared intermediate between small and large follicle cells with respect to gonadotropin-stimulated adenylate cyclase activities. The differential responsiveness of adenylate cyclase in porcine granulosa cells to FSH and LH (hCG) is consistent with gonadotropin effects on follicular cell development and changing adenylate cyclase activities can be important in the regulation of granulosa cell differentiation.