Modification by desipramine of the effects of alpha-adrenoceptor antagonists on the contractile responses of the trisected rat vas deferens.

Desipramine at 10(-7) M inhibited the neuronal uptake of noradrenaline and at 10(-6) M was also a alpha 1-adrenoceptor blocker. Desipramine potentiated and inhibited the responses of the epididymal and other portions to field stimulation, respectively, probably because the increased concentration of noradrenaline in the synapse was stimulating postjunctional alpha 1- and prejunctional alpha 2-adrenoceptors, respectively. Qualitatively the effects of prazosin, phentolamine and yohimbine on responses to added noradrenaline and to field stimulation were consistent with their being alpha 1-selective, nonselective and alpha 2-selective adrenoceptor antagonists. Quantitatively the effects of phentolamine and/or yohimbine on fast and slow responses to field stimulation and the modification of these effects by desipramine were dependent on the portion of vas, the response, the frequency of stimulation and the concentration of desipramine used.