Epinephrine-Sensitive Adenylyl Cyclase Activity in Rabbit Ovarian Tissues*

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Abstract
Epinephrine-sensitive adenylyl cyclase (AC) activity was investigated in homogenates of rabbit ovarian tissues. Optimal epinephrine-stimulated AC activity in corpora lutea homogenates was achieved with millimolar concentrations of ATP (1-4 mM) and Mg2+ (2-12 mM) in the absence of exogenously added Ca2+. Epinephrine stimulated the luteal AC under these conditions in a dose-dependent manner, with an ED50 of 0.45 .mu.g/ml. The AC of preovulatory follicle homogenates was unresponsive to epinephrine stimulation. Epinephrine responsiveness of the AC slowly appeared in late preovulatory and early postovulatory follicles in response to the gonadotropin surge induced by coitus. By 18 h after mating, epinephrine-stimulated AC activity had doubled, and maximal activities in the newly formed corpora lutea were reached within 72 h. Thereafter, epinephrine-stimulated AC activity gradually declined to a relatively stable value that was maintained throughout the remainder of gestation, except for 2 transient increases in activity on days 14 and 19 of pregnancy. With parturition, luteal epinephrine-stimulated AC activity fell to basal levels. In corpora lutea of pseudopregnancy, epinephrine-stimulated AC activity was very similar to that of corpora lutea of pregnancy during the first 16 days but fell to basal levels on day 17 with the termination of pseudopregnancy. Neither corpora albicans nor interstitial tissue exhibited any epinephrine-stimulated AC activity. The presence of epinephrine-stimulated AC activity only in corpora lutea of pseudopregnancy and pregnancy and not in preovulatory Graafian follicles, corpora albicans or intestitial tissue suggests a functional role for catecholamines in luteal tissue. The presence of an epinephrine-sensitive AC may be used as a functional marker for luteinization, at least in rabbit ovarian tissues.