Progesterone production by ectopic corpora lutea is independent of luteinizing hormone-stimulated adenylyl cyclase during early luteal development in the rabbit.

Abstract

Although estradiol is luteotropic in rabbits, corpora lutea develop and secrete progesterone in the absence of estradiol for 4-5 days. This period of estradiol independence is associated with high levels of LH-activated adenylyl cyclase and low levels of estradiol receptor. To determine if progesterone secretion is dependent on LH-stimulated adenylyl cyclase during this period of development, ectopic corpora lutea were established in ovariectomized rabbits. Rabbits were injected daily or twice daily with saline or 50, 100, or 150 IU hCG to desensitize LH-responsive adenylyl cyclase. On day 3, 4, 5, or 7, adenylyl cyclase activity was measured in luteal homogenates, and serum progesterone levels were determined by RIA. Basal and LH-stimulated adenylyl cyclase levels rose through day 5 of pseudopregnancy. Daily treatment with 50 or 100 IU hCG did not alter basal activity, but decreased LH-stimulated adenylyl cyclase activity by approximately 50% on day 3, by 80-90% on day 4, and by 90-95% on days 5 and 7. Serum progesterone levels were not different in hCG- and saline-treated rabbits. When LH-stimulated adenylyl cyclase was completely desensitized on days 3 and 4 of pseudopregnancy with twice daily injections of 150 IU hCG, serum progesterone levels were again, not different in saline- and hCG-treated rabbits. These results demonstrate that progesterone production by ectopic corpora lutea is not altered when LH-stimulatable adenylyl cyclase is desensitized and suggest that this early period of luteal development is independent of LH as well as estradiol.