A pharmacological investigation of the biphasic nature of the contractile response of rabbit and rat vas deferens to field stimulation.

It has been demonstrated previously with the vas deferens of the guinea-pig that the first and second phases of the contractile response to motor nerve stimulation are preferentially antagonized by the P2-purinoceptor antagonist arylazido aminopropionyl ATP (ANAPP3), and the alpha 1-adrenoceptor antagonist prazosin, respectively. We have now investigated the effect of the two antagonists on the biphasic contraction in the vas deferens of two other species; rabbit and rat. ANAPP3, in a concentration which antagonized responses to exogenously applied ATP but not those to exogenous norepinephrine, preferentially reduced the initial phasic response of the rabbit vas deferens to motor nerve stimulation without significantly reducing the secondary, tonic phase of the response. Prazosin had the opposite effect; antagonizing the response to norepinephrine but not to ATP and reducing the tonic response to motor nerve stimulation without significantly reducing the initial phasic response. Results obtained with the rat vas deferens were similar. The present results combined with previous findings suggest that ATP and norepinephrine act as cotransmitters in the vas deferens of several species.