Influence of oestrogens on muscarinic receptor density and contractile response in the guinea-pig uterus

The objective of this study was to investigate the contractile response in vitro of uterine and myometrial strips from control and oestrogen-treated guinea-pigs to carbachol. In addition, the muscarinic receptor parameters in subcellular preparations from the myometrium of the same animals were evaluated. Strips of guinea-pig uterus contract in response to carbachol in a concentration dependent manner and the effect of carbachol is independent of the presence of an intact endometrium. However, treatment with oestrogen reduces the response to carbachol, when expressed with respect to the effect of KCl. Measurement of the specific binding of [ 3 H]quinuclidinyl benzylate ([ 3 H]QNB) to myometrial membranes from control and oestradiol-treated immature guinea-pigs showed that oestradiol significantly decreased the number of specific binding sites of [ 3 H]QNB, but did not change the apparent affinity of specific [ 3 H]QNB binding. Moreover, the apparent affinity constants for the different antagonists showed a close similarity to those obtained at muscarinic receptors present in the myometrium from control and oestradiol-treated guinea-pigs.