Rabbit Follicular Adenylyl Cyclase Activity. II. Gonadotropin-Induced Desensitization in Granulosa Cells and Follicle Shells1

Abstract

A simultaneous decline in luteinizing hormone (LH)- and follicle stimulating hormone(FSH)-stimulated adneylate cyclase (AC) activities was reported in rabbit follicles exposed in vivo to a coital-induced surge of LH or a bolus of human chorionic gonadotropin (hCG). FSH-stimulable AC activity was measured using an FSH preparation which contained .apprx. 1% LH. To evaluate more precisely the role of FSH in follicular function in rabbits, AC activity was reevaluated using a highly purified fraction of FSH to measure FSH-stimulated AC activity. LH- and FSH-stimulable AC activities were measured both in rabbit follicular granulosa cells and in thecal cell-predominated follicle shells at various times after mating or after the injection of an ovulatory concentration of hCG. In follicle shells, LH-stimulated Ac rapidly fell during the 1st hour after mating or hCG injection; FSH-stimulated AC did not change. Both AC parameters declined to near basal levels by 7 h. The rate of AC desensitization was markedly different in granulosa cells. No significant changes in LH- or FSH-stimulated AC activities occurred during the first 2 h following either the endogenous surge of LH or the exogenous bolus of hCG; by 4.5 h, gonadotropin-stimulated AC activities were significantly (P < 0.001) reduced. When isolated granulosa cells were exposed in vitro for 60 min to either LH or FSH, both the homologous and the heterologous gonadotropin-stimulated Ac activities, respectively, were reduced by 50%. These results demonstrate different rates of AC desensitization in follicle shells to LH and FSH when a purified fraction of FSH is used to measure FSH-stimulated AC activity. They also reveal markedly different rates of AC desensitization to gonadotropins in vivo between granulosa cells and thecal shells. Indirect evidence suggests that the retarded rate of AC desensitization in granulosa cells may be attributable to the avascularity of this follicular compartment.