Adenylyl Cyclase Activities in Ovarian Tissues. IV. Gonadotrophin-Induced Desensitization of the Luteal Adenylyl Cyclase Throughout Pregnancy and Pseudopregnancy in the Rabbit and the Rat

Abstract

We measured the adenylyl cyclase (AC) activity in dissected CL and the responsiveness of the AC system to LH, FSH, and prostaglandin (PG)E1 at different times following the administration of high doses of hCG or hLH to pseudopregnant and pregnant rats and rabbits. In rabbits, ovulatory doses of hCG promoted desensitization of the AC system in both CL of pregnancy and CL of pseudopregnancy (PSP), but at varying rates. At least a 50% decline in the LH-stimulated AC system was demonstrable 2 h after the hCG injection in CL obtained during PSP and the first 18 days of pregnancy. However, after day 21, AC activity was unaltered at 2 or 24 h after hCG injection, necessitating as much as 72 h for the AC system to become desensitized to LH. It seems that CL in the last third of pregnancy are afforded partial protection from the desensitizing effects of hCG. This protective effect was found not to be conferred upon follicles contained in ovaries after day 21 of pregnancy or upon newly, hCG-induced 3-day-old CL in 24-day pregnant rabbit ovaries. hCG-induced desensitization of CL adenylyl cyclase in rabbits was prevented neither by cauterization of tertiary follicles not by the continued administration of estradiol-17beta (1.5 mug SC twice daily), suggesting that this effect of hCG is due to a direct interaction with the CL, and not due to interruption of the follicular estrogen supply. In rats, the injection of an ovulatory dose of hCG (50 IU SC into prepubertal rats; 50 IU ip plus 50 IU SC into mature rats) also induced desensitization of the AC system in ovaries of superovulated prepubertal rats and in CL of pseudopregnant and pregnant rats. Desensitization of the AC system was not detectable at 2 h, was 30% of total by 6 h, and was complete at 24 h after hCG injection. Both regression of the CL and desensitization of the AC system in CL are induced only by doses of hCG which are ovulatory and not subovulatory. Desensitization of AC appears to precede functional luteolysis, at least in the pseudopreganant rabbit. Thus, the apparent close association between hCG-induced luteolysis and the desensitization of the adenylyl cyclase system in CL would suggest that desensitization may be a marker for luteal regression.