The Porcine Ovarian Follicle: III. Development of Chorionic Gonadotropin Receptors Associated with Increase in Adenyl Cyclase Activity During Follicle Maturation

Abstract

Specific binding of human chorionic gonadotropin (hCG), and the HCG-sensitive adenylate cyclase of granulosa cells from small (1-2 mm), medium (3-5 mm) and large (6-12 mm) porcine ovarian follicles were studied. The number of hCG-binding sites per cell (n) increases during follicle maturation without a change in the binding affinity. The values for n were 300-400 for small, 1000-1600 for medium and 8200-10,000 for large-follicle cells. The dissociation constant is 2.4 .times. 10 -10M for all cells. HCG-sensitive adenylate cyclase was demonstrated in porcine granulosa cells. The adenylate cyclase system of granulosa cells becomes increasingly responsive to hCG stimulation during follicle development. Maximal adenylate cyclase activation by hCG (1 .mu.g/ml) was 240, 750, and 7000 molecules of cyclic AMP formed/s per cell, respectively, for small, medium and large follicle cells. The concentration of hCG giving half-maximal stimulation (1.0 .times. 10-9M) was similar for both large and medium follicle cells. An increase in hCG receptor sites per cell occurs during maturation of the porcine ovarian follicle with out change of binding affinity, and the increase in the number of hCG receptors correlates well with hCG-sensitive adenylate cyclase activity during follicle development.