The actions of cirazoline on the rat vas deferens.

The pre- and postsynaptic effects of the alpha 1-agonist cirazoline were assessed in epididymal and prostatic portions of the rat isolated vas deferens. Cirazoline produced a postsynaptic alpha 1-adrenoceptor mediated potentiation of the isometric contraction to single pulse field stimulation in both prostatic and epididymal portions. In epididymal portions, nifedipine (10 microM) greatly attenuated the postsynaptic alpha 1-receptor mediated potentiation of nerve mediated contractions, uncovering a presynaptic inhibitory action of cirazoline . No evidence was found for alpha 2-antagonism by cirazoline . It is concluded that the previously reported antagonism of the presynaptic inhibitory effects of clonidine was due to postsynaptic potentiation of nerve-mediated responses by cirazoline .