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

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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. Copyright © 1985. American Society of Animal Science . Copyright 1985 by American Society of Animal Science