Effects of estrogen and progesterone on adrenoceptors and cyclic nucleotides in rat uterus

The effects of estrogen and progesterone on adrenoceptors and cyclic nucleotides were studied in ovariectomized rat uterus. The effects on adrenoceptors were examined by measuring mechanical responses to noradrenaline and by binding site determinations with [3H]-dihydroergocryptine and [3H]-dihydroalprenolol. After acute administration of estradiol-17 beta, uterine cyclic GMP was progressively and significantly elevated, but cyclic AMP declined through it was not significant. Phentolamine suppressed this cyclic GMP elevation. Both acute and chronic treatments with estrogen increased the number of alpha-receptors. The increase in uterine cyclic GMP was related to the increase in alpha-stimulation as a result of increased alpha-receptors. Chronic treatment with estrogen increased the number of alpha-receptors. The alpha-effect induced by noradrenaline was bidirectional in the uterus treated with estrogen chronically; there was contraction in normal Tyrode's solution and relaxation in high K+ Tyrode's solution. In other hormonal group, either alpha- or beta-effects produced relaxation. Enhancement of the alpha- and beta-effects by estrogen is attributed to an increased number of the receptors. Acute treatment with estrogen decreased the responses of cyclic AMP to isoproterenol and mechanical reactivity. Progesterone also enhanced the beta-effect as a result of an increase in the number of beta-receptors.