Role of cyclic AMP in rat uterine inhibitory response to salbutamol during the natural oestrous cycle.

The rat uterus varies in its inhibitory response to beta-adrenoceptor agonists during the natural oestrous cycle. In the work reported here, the possible involvement of intracellular adenosine 3',5' cyclic monophosphate (cAMP) metabolism in the variation in rat uterine inhibitory response to the beta-adrenoceptor agonist salbutamol, has been investigated in isolated preparations from proestrus, oestrus, metoestrus and dioestrus phases of the oestrous cycle. Basal tissue cAMP concentrations were similar in uteri from all 4 phases. Salbutamol (1.5 x 10(-9) M - 5 x 10(-6) M) caused concentration-dependent increases in uterine cAMP content over the basal levels. However, there were no significant differences (p greater than 0.05) in the effects produced by salbutamol in the 4 phases. The cyclo-oxygenase inhibitor, flurbiprofen (in concentrations up to 10(-6) M) did not affect basal or salbutamol-stimulated cAMP levels during the oestrous cycle. In conclusion, our results suggest that the variation in rat uterine inhibitory response to salbutamol may not be due to: (a) changes in tissue cAMP function induced by prior exposure to endogenous oestrogen; (b) effect of intramurally generated prostaglandins on cAMP production, and (c) the differential action of the agonist on cAMP formation during the natural oestrous cycle.