OBJECTIVE To investigate whether membrane-bound hormone receptors in corpus luteum (CL) couple to one common adenylyl cyclase (AC) or whether each receptor is coupled to its own AC. METHODS Plasma membranes from rat CL were used to assess the coupling of hormone receptors to AC under conditions allowing full expression of the enzyme system. The response to hCG, prostaglandin E2 alpha (PGE2), and isoproterenol were analyzed. METHODS Adenylyl cyclase activity was monitored by the direct conversion of [infinity-32P]ATP into [32P]cyclic AMP. Results were expressed as pmol/min per mg membrane protein. RESULTS Addition of hCG (200 mIU), PGE2 (100 microM), and isoproterenol(100 microM) in the presence of a saturating (100 microM) concentration of guanine nucleotide resulted in a marked stimulation of the enzyme 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 individual effects. Thus, in the presence of the three hormones together, AC stimulation was 582 +/- 41 (n = 5), a value that was not significantly different from the stimulation observed with each hormone alone. CONCLUSIONS These data indicate that luteal membranes contain a single AC system. Therefore, hormone receptors couple and activate a common signal transducer AC in luteal membranes.