Regulation of gonadotropin-stimulable adenylyl cyclase of the primate corpus luteum.

In an effort to understand the molecular mechanisms that control luteal function in the human and nonhuman primates, we have investigated the experimental conditions for expression of gonadotropin-induced adenylyl cyclase (AC) in membrane particles from primate corpus luteum (CL) and some of the factors modulating the enzyme activity. We also examined the usefulness of the cell-free model for studying the role of AC in the regulation of CL functions in human and nonhuman primates. Enzyme activity was dependent on guanine nucleotide and Mg ion. Dose-response curves showed that the AC activation constants for hCG was about 0.1 microgram/ml. This value did not shift after the addition of guanine nucleotide. Enzyme responsiveness to prostaglandin E2 was small and, in contrast to a number of other nonprimate species, AC from the human CL was not stimulated by catecholamines. Calcium directly inhibited responsiveness of hCG-sensitive AC; inhibition was significant at 0.5 mM CaCl2 (in the presence of 1 mM EDTA and 2 mM ATP), being 90% at 2.5 mM CaCl2. These results support the concept that Ca2+ might play a role in the regulation of gonadotropin action and life span of human CL. Changes in AC activities during luteal phase and pregnancy were similar in the CL of monkeys and humans. Thus, in both cases, maximal gonadotropin responsiveness was observed during the midluteal phase. Also, during pregnancy (term and early pregnancies), responsiveness to exogenous hCG in vitro was very low, but the enzyme was readily responsive to NaF (10 mM) and forskolin (100 microM). These activities suggest that the tissue remains functionally active during pregnancy. It is concluded that the cell-free AC system is an effective model to study the cellular mechanisms that regulate luteal function in human and nonhuman primates.