Interactions of hormones stimulating and inhibiting uterine contraction were studied in vitro in uteri from oophorectomized rats. The beta-adrenergic effector, isoproterenol, a potent inhibitor of contraction, produced a dose-related increase of adenylate cyclase and accumulation of adenosine 3':5'-cyclic monophosphate (cAMP) that was inhibitable by propranolol. Oxytocin, which stimulates contraction, effectively inhibited accumulation of uterine cAMP induced by isoproterenol in the presence or absence of theophylline. Prostaglandins E(2) and F(2alpha), each at a maximum effective concentration of 0.5 muM, also inhibited accumulation of cAMP induced by isoproterenol, consistent with their effect in stimulation of uterine contraction. Prostaglandin E(2), but not prostaglandin F(2alpha), stimulated cAMP accumulation in a dose-related manner at concentrations in excess of 0.5 muM. Neither propranolol nor oxytocin inhibited that response. Bovine endometrial adenylate cyclase failed to respond to isoproterenol but was stimulated by prostaglandins E(1) and E(2). When myometrial preparations were studied, isoproterenol stimulation and prostaglandin effects were observed as for whole castrate uterus. The competitive physiological actions of beta-adrenergic effectors on the one hand, and oxytocin and prostaglandins on the other hand, are based on their influences on a myometrial adenylate cyclase. Stimulation of uterine cAMP accumulation by prostaglandin E(2) is due to action at a different and unrelated site.