Identification of α 1-adrenoceptor subtypes involved in contraction of young CD rat epididymal vas deferens

Abstract

Contraction of rat epididymal vas deferens is regulated via a release of neurotransmitters from autonomic nerves and is mediated by α 1-adrenoceptors. This study was directed to the characterization of α 1-adrenoceptors involved in the contraction of the epididymal portion of young CD rat vas deferens, that were selectively discriminated in two populations through the irreversible blockade of two β-chloroethyamines, 1 and 2. The antagonist activity of known subtype-selective α 1-adrenoceptor antagonists, WB4101, 5-MU, and RS17053 (α 1A), (+)-cyclazosin (α 1B), and BMY7378 (α 1D), was evaluated in the α 1-adrenoceptors of the studied tissue as such and after pre-treatment with a proper discriminating concentration of β-chloroetylamines 1 and 2, comparing the results with the affinities determined in classical Wistar rat models: prostatic vas deferens (α 1A), spleen (α 1B), and thoracic aorta (α 1D). The results suggested that two α 1A-adrenoceptors are involved in the contraction of the epididymal vas deferens of young CD rats. These may represent two α 1A-adrenoceptor isoforms that are selectively and irreversibly blocked by β-chloroetylamines 1 and 2, and reversibly antagonized by RS17053. The minor population, preferentially blocked by 1, seems correspond to a classical α 1A-adrenoceptor subtype, while the major population, preferentially blocked by 2 and antagonized by RS17053 with low affinity, seems to correspond to an α 1L-adrenoceptor.