Effects of luteinizing hormone-releasing hormone agonist and calcium upon adenylyl cyclase activity of human corpus luteum membranes |
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| Authors: | F J Rojas R H Asch |
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| Affiliation: | 1. Department of Agricultural and Forestry Sciences, University of Tuscia, 01100 Viterbo, Italy;2. Department of Horticulture and Landscape Architecture, Purdue University, 625 Agriculture Mall Drive, West Lafayette, IN, United States;3. Department of Vegetable Crops, Agricultural Research Institute, 1516 Nicosia, Cyprus;4. Department of Agricultural Sciences, University of Naples Federico II, 80055 Portici, Italy;1. State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai, 200092, China;2. Department of Civil and Environmental Engineering, William & Cloy Codiga Resource Recovery Center, Center for Sustainable Development & Global Competitiveness, Stanford University, Stanford, CA, 94305-4020, USA;1. Hunan University of Technology, Zhuzhou 412007, China;2. Queensland University of Technology, Queensland 4001, Australia;1. Programa de Pós-Graduação em Neurociências, Universidade Federal de Minas Gerais (UFMG), Belo Horizonte, MG, Brazil;2. Departamento de Clínica Médica, Faculdade de Medicina, UFMG, Belo Horizonte, MG, Brazil;3. Neuropsychiatry Program, Department of Psychiatry and Behavioral Sciences, McGovern Medical School, The University of Texas Health Science Center at Houston, Houston, TX, USA;4. Santa Casa BH Ensino e Pesquisa, Belo Horizonte, MG, Brazil;1. Key Laboratory of New Energy and Rare Earth Resource Utilization of State Ethnic Affairs Commission, Key Laboratory of Photosensitive Materials & Devices of Liaoning Province, School of Physics and Materials Engineering, Dalian Minzu University, 18 Liaohe West Road, Dalian, 116600, China;2. Department of Physics, Dalian Maritime University, Dalian, Liaoning, 116026, China;1. Department of Microtechnology for Biology and Health, CEA LETI – Minatec, 17 rue des Martyrs, 38054 Grenoble Cedex 9, France;2. SATIE, CNRS, ENS Cachan, 61 avenue du Président Wilson, 94235 Cachan Cedex, France;3. bioMerieux, Technology Research Department, 5 rue des Berges, 38000 Grenoble, France |
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| Abstract: | We have investigated the ability of the agonist analog of luteinizing hormone-releasing hormone (LH-RH), D-Trp6-LH-RH (LH-RHa), and of CaCl2 to inhibit directly gonadotropin stimulation of adenylyl cyclase in a cell-free system prepared from human corpus luteum. In the presence of a submaximally effective concentration of hCG, addition of 10(-5)M final concentration of LH-RHa did not alter the gonadotropin-stimulated enzyme activity, nor did LH-RHa alone show any effect upon basal levels of the enzyme. The failure to inhibit adenylyl cyclase would indicate that the LH-RHa does not affect gonadotropin receptor binding or cAMP synthesis and/or degradation in this membrane system, suggesting that the luteolytic effects of LH-RH are unlikely to involve a direct antigonadotropic activity at the level of the human corpus luteum. In great contrast to LH-RHa, addition of CaCl2 resulted in a dose-dependent inhibition of hCG-stimulable adenylyl cyclase. Thus, in the presence of either a maximally or submaximally effective concentration of hCG, inhibition was significant at 0.5 mM CaCl2 added in excess of ATP (2 mM) and EDTA (1 mM), being about 90% upon addition of 2.5 mM CaCl2. We also found that calcium reduced enzyme stimulation by forskolin and the GTP analog, guanyl 5'-yl imidodiphosphate [GMP-P(NH)P] in a dose-related manner and that activation by NaF was less sensitive to inhibition by calcium. Accordingly, at 2.5 mM CaCl2, guanyl nucleotide and forskolin stimulations were inhibited 96% and 86%, respectively, while NaF stimulation was reduced by 40%. Because previous studies have shown that calcium does not impair gonadotropin binding activity, the calcium-dependent inhibition of gonadotropin responsiveness reported here would imply an alteration in the functional coupling of the components of the luteal adenylyl cyclase system. These data suggest that calcium may play a role in the regulation of gonadotropin action in the human corpus luteum. |
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