Regional differences in the adenosine A 2 receptor-mediated modulation of contractions in rat vas deferens

Abstract

Adenosine receptors involved in modulation of contractions were characterized in the bisected rat vas deferens by combining pharmacological and immunohistochemical approaches. In both portions, noradrenaline-elicited contractions were enhanced by the adenosine A 1 receptor agonist N 6-cyclopentyladenosine (CPA), and inhibited by the non-selective adenosine receptor agonist 5′- N-ethylcarboxamidoadenosine (NECA) in the presence of the adenosine A 1 receptor antagonist 1,3-dipropyl-8-cyclopentyl-l,3-dipropylxanthine (DPCPX). The adenosine A 2A receptor agonist 2- p-(2-carboxyethyl)phenethyl-amino-5′- N-ethylcarboxamidoadenosine (CGS 21680) also inhibited noradrenaline-elicited contractions but only in the prostatic portion. Contractions elicited by the stable ATP analogue α,β-methyleneATP (α,β-MeATP) were inhibited only by NECA in the presence of DPCPX and only in the prostatic portion. This study provides functional evidence for the presence, in both portions of the rat vas deferens, of an adenosine A 1 receptor-mediated enhancement and of an adenosine A 2 receptor-mediated inhibition of contractions. The latter effect is mediated by both A 2A and A 2B subtypes in the prostatic portion but only by the A 2B subtype in the epididymal portion. This regional variation is supported by the immunohistochemical results that revealed an adenosine A 2A receptor immunoreactivity not co-localized with nerve fibres more abundant in the prostatic than in the epididymal portion.