Rabbit follicular adenylyl cyclase activity. II. Gonadotropin-induced desensitization in granulosa cells and follicle shells.

Abstract

Previous studies reported a simultaneous decline in luteinizing hormone (LFI)- and follicle stimulating hormone(FSH)-stimulated adenylyl cyclase (AC) activities in rabbit follicles exposed in vivo to a coital-induced surge of LH or a bolus of human chorionic gonadotropin (hCG) (HunzickerDunn and Birnbaumer, 1976). In these studies, FSH-stimulable AC activity was measured using an FSH preparation which contained “.‘l% LH (Reichert and Wilhelrni, 1973). In an effort to evaluate more precisely the role of FSH in follicular function in rabbits, AC activity has been reevaluated using a highly purified fraction of FSH to measure FSH-stimulated AC activity. LH- and FSHstimulable AC activities were measured both in rabbit follicular granulosa cells and in thecal cell-predominated follicle shells at various times after mating or the injection of an ovulatory concentration of hCG. In follicle shells, LH-stimulated AC rapidly fell during the first hour after mating or hCG injection while 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, but by 4.5 h gonadotropin-stimulated AC activities were significantly (P<0.001) reduced. However, when isolated granulosa cells were exposed in vitro for 60 mm to either LU or FSH, both the homologous and the heterologous gonadorropin-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 granuloss cells may be attributable to the avascularity of this follicular compartment.