Β‐adrenoceptors in Circular and Longitudinal Myometrial Membranes and in Lung Membranes From Dioestrous and Post‐partum Guinea‐pigs

Abstract

1. We have examined the binding of (-)[125]-cyanopindolol ((-)[125I]-CYP) to membranes prepared from uterus and lung of dioestrous and post-partum (1-6 days) guinea-pigs. 2. The densities of beta-adrenoceptor binding sites in circular and longitudinal myometrium from dioestrous animals were similar, and approximately one-eight of those in the lung. Ascorbate and ethylenediaminetetraacetic acid in the incubation medium did not affect binding. 3. The numbers and affinities of beta-adrenoceptor binding sites in both myometrial layers and in lung parenchyma from post-partum animals were similar to those in corresponding tissues from dioestrous animals. 4. The distribution of beta-adrenoceptor binding sites in the post-partum uterus was examined using receptor autoradiography. Binding to circular and longitudinal muscle layers and to the endometrium was inhibited by (-)-propranolol (1 mumol/l), by the beta 2-adrenoceptor selective antagonist ICI 118,551 (70 nmol/l), but not by the beta 1-adrenoceptor selective antagonist CGP 20712A (100 nmol/l), indicating that the beta-adrenoceptor present was of the beta 2-subtype. 5. The ability of isoprenaline to compete for (--)[125]-CYP binding sites in uterine membranes from post-partum animals was approximately twice that in corresponding preparations from dioestrous animals. 6. Changes in the numbers or affinity of beta 2-adrenoceptors cannot account for the marked and selective enhancement of the actions of sympathomimetic amines at beta-adrenoceptors previously observed in longitudinal myometrium taken from post-partum guinea-pigs. It is suggested that enhancement of later steps in the chain of events between beta-adrenoceptor occupancy and uterine relaxation, and/or a decrease in the contribution of alpha-adrenoceptors to the net effect of the amine might provide alternative explanations.

α1‐ AND α2‐ADRENOCEPTORS OF THE CIRCULAR MYOMETRIUM FROM THE DIOESTROUS GUINEA‐PIG

“…1983a, b). The present Schild analysis ofthe antagonism ofphenylephrine by phentolamine and prazosin suggest that, in the presence of nisoxetine to block neuronal uptake, and of ICI 1 18,55 1 to block the p2-adrenoceptors present (Handberg et al 1988), it acts exclusively at al-adrenoceptors to produce contractions. Thus the pA2 values obtained for each of the a-adrenoceptor antagonists using this agonist on circular myometrium are similar to those obtained in other tissues in which al-adrenoceptors are present (Starke 198 1).…”