Luteal Adenylyl Cyclase Does Not Develop Sensitivity to Desensitization by Human Chorionic Gonadotropin in the Absence of Nonluteal Ovarian Tissue*

There is evidence suggesting that the mere presence of a hormone-responsive adenylyl cyclase system in a tissue may not be sufficient for desensitization to occur since phosphorylation reactions might also be involved. The purpose of this study was to determine if luteal tissue in the absence of other ovarian tissues would desensitize to human CG (hCG). One or both ovaries were removed from rabbits 5 h before hCG-induced ovulation and the periovulatory follicles were transplanted underneath the kidney capsule where they formed ectopic corpus luteum [or corpora lutea (CL)]. Rabbits which were bilaterally ovariectomized received estradiol implants at the time of ovariectomy to maintain control serum estradiol concentrations. On day 7 of pseudopregnancy, the rabbits were injected with saline (control) or with 75 IU hCG and were killed 24 h later at which time ovarian and ectopic CL progesterone content and adenylyl cyclase activity were assessed. As expected, in ovarian CL there was decreased LH-responsive adenylyl cyclase (69% relative to control) and a correspondingly decreased luteal progesterone content (40% relative to control). In the same rabbits, the ectopic CL showed much the same pattern of response as the ovarian CL but perhaps to a slightly lesser extent (decreases relative to control of 59% in adenylyl cyclase response to LH and 29% in progesterone content). However, in rabbits with ectopic CL only, the luteal tissue showed no change either in hormone-responsive adenylyl cyclase activity or in progesterone content. Similarly, binding of radiolabeled hCG to luteal membranes 24 h after hCG was almost totally absent in ovarian CL, was decreased by 50% in ectopic CL with one ovary present, and was unaltered in ectopic CL of bilaterally ovariectomized rabbits. These data suggest that nonluteal ovarian tissue may be required for the induction in CL of the appropriate protein kinases for the proposed phosphorylations involved in adenylyl cyclase desensitization.