Endocrinology, Vol 126, 1191-1198, Copyright © 1990 by Endocrine Society

ARTICLES

Comparison of the luteinizing hormone-sensitive adenylyl cyclase of the pig ovarian follicle and corpus luteum and its susceptibility to in vitro hormone-dependent desensitization

RC Ekstrom and M Hunzicker-Dunn
Department of Molecular Biology, Northwestern University Medical School, Chicago, Illinois 60611.

The hormone responsiveness of the adenylyl cyclase of pig ovarian follicles or corpora lutea was examined. Adenylyl cyclase activity was assayed in 10,000 x g membrane fractions that had been prepared with or without (control) a urea extraction. In control luteal membranes there was little stimulation (less than 2-fold) or adenylyl cyclase by saturating ovine (o) LH, hCG, or (-)isoproterenol in the absence or presence of 10 microM GTP. However, in urea-treated luteal membranes, a 2- to 3-fold stimulation of adenylyl cyclase was caused by saturating oLH or hCG, and a 4- to 5-fold stimulation by (-)isoproterenol; the marked stimulation by the gonadotropins was only observed if 10 microM GTP was added. In follicular membranes, a 3- to 4-fold stimulation of adenylyl cyclase by gonadotropins was observed regardless of whether GTP was added or the membranes had been urea extracted. Stimulation of adenylyl cyclase by (-)isoproterenol was always less than 2-fold in follicular membranes. The binding affinity for [125I]hCG was similar in control follicular and luteal membranes, but there were approximately 10-fold more [125I]hCG-binding sites in follicular compared with luteal membranes. The binding affinities and number of receptor sites were not significantly changed by urea treatment. The ED50 values for hCG or (- )isoproterenol were the same in follicular and luteal membranes and were uneffected by the addition of 10 microM GTP, but the ED50 for oLH was 3-fold lower in follicular than in luteal membranes. GTP caused a dose-dependent increase in adenylyl cyclase activity in luteal and follicular membranes, and both tissues had the same ED50. A saturating hormone concentration resulted in an approximately 2-fold decrease in the ED50 for GTP. In vitro hCG-induced desensitization of the hCG- responsive adenylyl cyclase was 31% in follicular membranes, but only 11-15% in luteal membranes. Hormone-induced desensitization was not increased in incubations of luteal homogenate or membranes plus cytosol. These results establish the existence of a LH/hCG-sensitive adenylyl cyclase in the pig corpus luteum and indicate that the G- protein and catalytic moieties of the follicular and luteal adenylyl cyclase complex are functionally the same, but some difference exists in the way the LH/hCG-receptor in the two tissues interacts with the G- protein/catalytic complex.

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