Prazosin selectively inhibits the responses to field stimulation in the rat vas deferens.

The effects of prazosin on contractile responses of the epididymal and prostatic halves of the rat vas deferens have been studied. In the epididymal half responses to acetylcholine were not altered by hexamethonium, 100 microM, but were inhibited by atropine, 10 nM. Prazosin, 100 nM, had no effect on maximal or submaximal responses to acetylcholine or methacholine. In the presence of cocaine, 10 microM, prazosin 10 and 100 nM, reduced the magnitude of the maximal twitch and sustained responses to field stimulation in the epididymal and prostatic halves of the vas deferens. Submaximal responses at all frequencies of stimulation and to exogenously applied noradrenaline were also inhibited by prazosin. Thus all responses to field stimulation of the epididymal and prostatic halves of the vas deferens are susceptible to selective alpha 1-adrenoceptor blockade with low concentrations of prazosin.