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Changes and Interrelationships among Luteal LH Receptors, Adenylate Cyclase Activity and Phosphodiesterase Activity during the Bovine Estrous Cycle¹

University of Missouri, Columbia 65211

Abstract

Changes and interrelationships among the cellular mechanisms that may regulate luteal progesterone synthesis during the bovine estrous cycle were studied. Corpora lutea (CL) were enucleated from 30 cows via a transvaginal incision on d 4 7, 10, 13, 16 and 19 following estrus (estrus = d 0). Mean corpus luteum weight, and luteal progesterone and plasma progesterone concentrations increased (P<.05) from d 4 to 7 or 10, and declined following luteal regression (d 19). Unoccupied LH receptor (UOR) concentrations increased (P<.05) more than fourfold from d 4 (38 fmol/mg protein) to d 16 (173 fmol/mg protein) before declining (P<.05) by d 19 (30 fmol/mg protein). The dissociation constant for UOR concentrations increased (P<.05) during the estrous cycle. Concentrations of occupied LH receptors (OR) were less (P<.05) on d 7 than other days; however, the total number of OR/CL increased fourfold from d 4 (47 fmol/CL) to d 10 (221 fmol/CL) and remained similar thereafter. Basal adenylate cyclase, LH-activated adenylate cyclase, and Gpp(NH)p-activated adenylate cyclase activities were greatest (P<.05) on d 7 to 16 as compared with d 4 and 19. Luteinizing hormone stimulated (P<.05) adenylate cyclase activity relative to basal activity on d 7, 10, 13, and 16; whereas, Gpp(NH)p stimulated (P<.05) adenylate cyclase activity relative to basal activity at each period. Phosphodiesterase was 46% greater on d 19 as compared with d 4. Plasma progesterone concentrations were positively correlated (P<.01) with UOR concentrations (r = .64), basal adenylate cyclase (r = .46), LH-activated adenylate cyclase (r = .52) and Gpp(NH)p-activated adenylate cyclase (r = .47) activities. Although progesterone was not correlated with OR concentrations, the total OR/CL was positively correlated (r = .43, P<.01). The UOR concentrations, basal adenylate cyclase, LH-activated adenylate cyclase and Gpp(NH)p-activated adenylate cyclase activities were greatest from d 7 to 16 of the estrous cycle and were positively correlated with plasma progesterone concentrations.

¹ Contribution from the Missouri Agr. Exp. Sta. Journal Ser. No. 9684.

² Dept. of Dairy Sci.

³ Reprint Requests.

⁴ Dept. of Anim. Sci.

⁵ Dept. of Vet. Med. and Surg.; present address: Large Animal Med. and Surgery, College of Vet. Med., Texas A&M Univ., College Station, TX 77843.

⁶ Dept. of Biochem.

⁷ The authors wish to express their appreciation to Dr. D. J. Bolt, for supplying purified bovine FSH (Grimek et al., 1979); to Dr. J. G. Pierce, for supplying purified bovine TSH; and to the NIAMD, for supplying purified bovine prolactin (NIH-P-B5) and growth hormone (NIH-GH-B18) for determining specificity of the cell membrane preparations to LH. The purified HCG (CR-121) was a gift from the Center for Population Research of NICHHD.