FSH-Responsive Adenylyl Cyclase in Rat Testes: Desensitization by Homologous Hormone

Abstract

Injection of high doses of FSH causes a partial desensitization of the FSH-responsive adenylyl cyclase (AC) in adult rat testes. The loss of responsiveness to FSH is dependent on time. Two hours after injection of one dose of human FSH (256 μg hFSH-PT₂) in vivo, no effect was seen on FSH-stimulated AC activity (K_m and maximal activation). After 24 hr there was an approximately 40% decrease in FSH activated AC. Injection of two doses of FSH (256 μg hFSH-PT₂) 24 and 48 hr before being killed, gave a loss in FSH-responsive AC activity of approximately 60%. The decreased FSH-stimulated AC activity after FSH injections in vivo was associated with a comparable decrease in specific FSH binding. Whether this is a reflection of receptor occupancy or down regulation of the number of FSH receptors is not known. Desensitization of the FSH-responsive AC caused by FSH was not associated with a change in its K_m.