Contractions of rat vas deferens are mediated by α1A‐ and α1D‐adrenoceptors

Abstract

The subtypes of α1‐adrenoceptor mediating contractions of rat vas deferens to exogenous noradrenaline have been examined employing the α1A‐adrenoceptor antagonist RS100329 and α1D‐adrenoceptor antagonist BMY7378. In the presence of cocaine (3 μM) to block the noradrenaline transporter, the potency of noradrenaline at producing contractions was significantly increased in epididymal but not prostatic portions, and the effect was mainly in terms of phasic contractions. RS100329 produced approximately parallel shifts in the potency of noradrenaline at producing tonic contractions in epididymal portions in the absence of cocaine, but produced non‐parallel shifts in the presence of cocaine. In epididymal portions, BMY7378 showed high potency against phasic contractions to noradrenaline in the presence but not the absence of cocaine. It is concluded that the predominant tonic contraction to noradrenaline in epididymal portions of rat vas deferens is mediated by α1A‐adrenoceptors, but α1D‐adrenoceptors are additionally involved in phasic contractions. These phasic contractions are amplified by cocaine, suggesting that blockade of the noradrenaline transporter makes α1D‐adrenoceptors available to exogenous noradrenaline.