EVIDENCE THAT HORMONE RECEPTORS COUPLE AND ACTIVATE A COMMON SIGNAL TRANSDUCER ADENYLYL-CYCLASE IN CORPUS-LUTEUM

Objectives: To investigate whether membrane-bound hormone receptors in corpus luteum (CL) couple to one common adenylyl cyclase (AC) or whet her each receptor is coupled to its own AC. Design: Plasma membranes f rom rat CL were used to assess the coupling of hormone receptors to AC under conditions allowing full expression of the enzyme system. The r esponse to hCG, prostaglandin E(2) alpha (PGE(2)), and isoproterenol w ere analyzed. Main Outcome Measure: Adenylyl cyclase activity was moni tored by the direct conversion of [proportional to-P-32]ATP into [P-32 ]cyclic AMP. Results were expressed as pmol/min per mg membrane protei n. Results: Addition of hCG (200 mIU), PGE(2) (100 mu M), and isoprote renol(100 mu M) in the presence of a saturating (100 mu M) concentrati on of guanine nucleotide resulted in a marked stimulation of the enzym e compared with controls, reaching 552 +/- 28, 537 +/- 42, and 558 +/- 32 (mean +/- SEM), respectively. Addition of hormones in pairs or all three together did not result in an additive response of the individu al effects. Thus, in the presence of the three hormones together, AC s timulation was 582 +/- 41 (n = 5), a value that was not significantly different from the stimulation observed with each hormone alone. Concl usion: These data indicate that luteal membranes contain a single AC s ystem. Therefore, hormone receptors couple and activate a common signa l transducer AC in luteal membranes.