Mediaton of contraction in rat cauda epididymidis by alpha-adrenoceptors

Abstract

Subtypes of alpha-adrenoceptors responsible for contractions of the rat cauda epididymidis were studied in vivo by micropuncture using a servo-nulling pressure transducer system. Administration of both non-selective and selective alpha-adrenoceptor agonists in doses of 1-40 μg noradrenaline kg-1body weight (BW), 1-100 μg clonidine kg-1BW, or 100-800 μg methoxamine kg-1BW enhanced contractions of the proximal cauda epididymidis in a dose-response manner. The potency of the agonists were noradrenaline ≥ clonidine > methoxamine. Pretreatments with selective α1-adrenoceptor antagonist (prazosin) and α2-adrenoceptor antagonist (yohimbine) at the doses of 400 and 800 μg kg-1BW, respectively, had very little effect on spontaneous contractions, but effectively blocked the responses to the maximal doses of methoxamine and clonidine. The responses could not be explained by the systemic effects of agonists and antagonists. The results suggest that contraction of the proximal cauda epididymidis of rats is mediated by both α1- and α2-adrenoceptors. The latter appears to be more abundant.