INFLUENCE OF ESTROGENS ON MUSCARINIC RECEPTOR DENSITY AND CONTRACTILERESPONSE IN THE GUINEA-PIG UTERUS

The objective of this study was to investigate the contractile respons e in vitro of uterine and myometrial strips from control and oestrogen -treated guinea-pigs to carbachol. In addition, the muscarinic recepto r parameters in subcellular preparations from the myometrium of the sa me animals were evaluated. Strips of guinea-pig uterus contract in res ponse 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, w hen expressed with respect to the effect of KCl. Measurement of the sp ecific binding of [H-3]quinuclidinyl benzylate ([H-3]QNB) to myometria l membranes from control and oestradiol-treated immature guinea-pigs s howed that oestradiol significantly decreased the number of specific b inding sites of [H-3]QNB, but did not change the apparent affinity of specific [H-3]QNB binding. Moreover, the apparent-affinity constants f or the different antagonists showed a close similarity to those obtain ed at muscarinic receptors present in the myometrium from control and oestradiol-treated guinea-pigs.