The Effect of Estradiol on Hormonally Stimulable Adenylyl Cyclase Activity and on Progesterone Production in Normal and Regressing Corpora Lutea from Control and Human Chorionic Gonadotropin-Treated Pseudopregnant Rabbits*

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Abstract
The effect of administering a luteolytic dose of hCG (100 IU, iv) to 9-day pseudopregnant rabbits that received either no other treatment (controls) or one of two estradiol (E-1.5 or E-15) treatments was studied. E-1.5 and E-15 consisted of 1.5 μg estradiol (E) every 12 h and 15 μg E every 12 h, respectively; these treatments were administered sc in sesame seed oil starting at 2200 h on day 8 and continued through 2200 h on day 11. Animals were bled daily from days 9–12 and sacrificed between 1000–1100 h on day 12, at which time serum and corpora lutea (CL) progesterone content, weight, and adenylyl cyclase activities stimulated by LH (10 μg/ml) and isoproterenol (Iso; 10−4m) were determined. We found that 1) neither low (E-1.5) nor high (E-15) E treatment prevented functional luteolysis (drop in serum progesterone) induced by hCG; 2) E-15 but not E-1.5 prevented structural luteolysis (CL weight loss) induced by hCG; 3) E-15 but not E-1.5 resulted in CL progesterone levels that, after hCG, were indistinguishable from levels in CL of control animals that received either no treatment or E-15 alone; 4) hCG on day 9 alone resulted, by day 12, in the loss of both LH-stimulable and Iso-stimulable CL adenylyl cyclase activities; 5) E-1.5 had no effect on CL adenylyl cyclase activity and did not protect against hCG; 6) E-15 alone resulted, by day 12, in the appearance of a partially but significantly decreased LH-stimulable activity without affecting either basal or Iso-stimulable activities; and 7) LH and Iso-stimulable activities in CL of E-15-treated rabbits did not differ upon hCG treatment. We conclude 1) that hCG and LH affect rabbit CL by stimulating adenylyl cyclase, desensitizing adenylyl cyclase, and triggering functional luteolysis; 2) that the luteolytic effect of hCG is direct and independent of E supply; 3) that high doses of E (E-15) but not low doses of E (E-1.5) can protect the CL against the effects of hCG resulting in the loss of hormone-stimulable adenylyl cyclase activities and against the structural luteolysis that follows hCG-induced functional luteolysis; and 4) that progesterone synthesis and secretion in CL may be separately and independently regulated by LH, thus accounting for low serum progesterone in rabbits treated with E-15 plus hCG in spite of the presence of tissue progesterone levels similar to those seen in actively secreting CL of control or E-15 only-treated rabbits. (Endocrinology106: 375, 1980)