| Abstract: | Gonadotropin receptor sites and adenylate cyclase activity were analyzed in luteinized rat ovaries following injection of human chorionic gonadotropin (hCG). Gonadotropin binding capacity and hormonal stimulation of adenylate cyclase declined rapidly to a minimum at 6 to 12 h, remained depressed for 4 days, and returned to the control level between 5 and 7 days. Total adenylate cyclase activity measured in the presence of fluoride fell by 50% within a few hours but returned to normal by 24 h. A close correlation was observed between the number of gonadotropin receptors and the ability of adenylate cyclase to be stimulated by hormone. Assay of tissue-bound hormone showed that the initial loss of hormone sensitivity and binding capacity was associated with occupancy of luteinizing hormone receptor sites, but that the prolonged changes in these activities were not attributable to receptor occupancy. These studies have demonstrated that induction of a refractory or desensitized state in ovarian adenylate cyclase by gonadotropin results from the loss of specific hormone receptor sites. |
