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

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Abstract
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 [norepinephrine, NE] and by binding site determinations with [3H]-dihydroergocryptine and [3H]-dihydroalprenolol. After acute administration of estradiol-17.beta., uterine cGMP was progressively and significantly elevated, but cAMP declined though it was not significant. Phentolamine suppressed this cGMP elevation. Both acute and chronic treatments with estrogen increased the number of .alpha.-receptors. The increase in uterine cGMP was related to the increase in .alpha.-stimulation as a result of increased .alpha.-receptors. The .alpha.-effect induced by NE 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 the 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 cAMP to isoproterenol and mechanical reactivity. Progesterone also enhanced the .beta.-effect as a result of an increase in the number of .beta.-receptors.

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