Increased density of α-adrenoceptors in vas deferens of spontaneously hypertensive rats (SHR), indicated by functional and receptor binding studies

Abstract

Pharmacological parameters were determined from conractile responses mediated by α-adrenoceptors in vas deferens from spontaneously hypertensive rats (SHR) and corresponding normotensive controls, Wistar Kyoto rats (WKY), and compared with data obtained from radioligard binding assays. Contractile responses induced in longitudinal and circular muscle layers by the α-adrenoceptor agonist noradrenaline (NA) and by barium chloride were recorded as described previously. In both muscle layers the maximal effects induced by NA, but not by BaCl 2, were significantly greater in SHR. As a consequence, the relative responsiveness ratio (ϱ) for the α-adrenoceptor was also larger for SHR than for WKY. NA-induced contractions of both muscle layers were competitively antagonized by indoramine. The pA 2 values for indoramine and pD 2 values for NA were the same in SHR and WKY, indicating that α-adrenoceptor affinity was not changed in SHR. Additionally, binding studies with the α-adrenoceptor ligand [ 3H]WB4101 revealed that B max values were greater in the vas deferens of SHR, whereas K d values were not significantly different from those of WKY controls. In summary, although differences could not be detected for affinity-related parameters, a greater density of α-adrenoceptors was shown for SHR in receptor binding studies and this was corroborated by functional studies.