Interconversion of Agonist-Induced Responses of Prostatic and Epididymal Portions of the Rat Vas Deferens Induced by Castration

Abstract

The influence of castration (30-90 days) on the effects of ATP, noradrenaline (Nor), and carbachol (CCh) were examined in prostatic and epididymal portions of the rat vas deferens. All agonist-induced contractions were greatly increased in the prostatic and suppressed in the epididymal portion of the vas deferens from castrated rats, as compared with those in preparations from normal animals. Responses to Nor showed a typical cumulative dose–effect curve, with an additional twitch at the minimal dose. Responses to CCh were paradoxically changed; the maximum of twitch responses was observed at threshold concentrations (10-7 to 3 · 10-7 M), and decreased at higher concentrations. In the threshold concentration (10-7 M), ATP induced almost maximal responses in a non-cumulative manner. All agonist-induced responses were blocked by isradipine (10-7 M) and increased by pretreatment with reserpine. In normal animals, injection of testosterone insignificantly decreased responses to all agonists. The ratio of the amplitude of high-potassium (80 mM)-induced contractions (mm) to the tissue wet mass (per mg) in preparations from castrated animals also showed oppositely directed modulation of the responses, as compared with that in normal animals. It is suggested that the lack of hormone modifies a negative feedback mechanism of elevation of the intracellular Ca2+ concentration, which exists in normal rats mostly in the prostatic portion and is the reason for regional variation along the vas deferens, to a positive feedback link amplified in castrates.