Avaliação dos efeitos da histamina na contração do ducto epididimário da cauda do epidídimo de rato

Abstract

The motor activity of the epididymal duct is an essential process for male fertility, as it results in the correct transport, maturation, storage and emission of spermatozoa. This process is regulated by hormonal (testosterone, vasopressin, oxytocin), neuronal (adrenergic and cholinergic autonomic innervation), and epithelial (endothelin-1, NO, serotonin, prostaglandins, angiotensin, etc.) mechanisms. However, although there is evidence for the presence of histamine in the epididymis, its modulatory effects on the motor activity of the epididymal duct are not yet known. Thus, the objective of this work was to evaluate the effects of histamine on contractions of the rat distal cauda epididymis duct by identifying histaminergic receptors and the participation of autonomic neurotransmitters. To achieve these objectives, segments of the epididymal duct from the distal cauda of the epididymis of Wistar rats were isolated and used in functional experiments in an isolated organ bath to evaluate the direct effects of histamine on epididymal duct or adrenergic agonist-induced contractions. These experiments were also performed in the presence of selective antagonists for histaminergic receptors (H1, H2 and H3), α1-adrenoceptors and muscarinic receptors. We found that histamine produced contractions of a phasic nature. The frequency and amplitude of histamine-induced phasic contractions in the epididymal duct were inhibited by promethazine (H1 receptor antagonist), ranitidine (H2 receptor antagonist), atropine (muscarinic receptor antagonist) or prazosin (α1-adrenoceptor antagonist). Histamine potentiated the contractile effects of noradrenaline and reduced its maximal effect, and these effects were prevented by ranitidine and promethazine, respectively. We conclude that histamine is able to promote phasic contractions with the participation of H2 receptors and release of autonomic neurotransmitters. Furthermore, this biogenic amine modified noradrenaline-induced epididymal duct contractions with the possible participation of H1 and H2 receptors.