1. Electrical and mechanical responses of epididymal and prostatic regions of rat, rabbit and guinea-pig vas deferens have been examined to investigate regional variation in purinergic and adrenergic mechanisms. 2. Noradrenaline was significantly more potent in producing contraction in epididymal segments of the muscle than in prostatic segments. 3. ATP and alpha,beta,methylene ATP were significantly more potent in producing contraction of prostatic segments than epididymal segments. 4. In guinea-pig vas deferens the resting membrane potential was greater in smooth muscle cells in the prostatic region than in the epididymal. Excitatory junction potentials (EJPs) in both the epididymal and prostatic regions were of similar magnitude and were almost abolished by the P2x-purinoceptor antagonist suramin. 5. The alpha-adrenoceptor antagonist phentolamine had no inhibitory action on EJPs in either region of the guinea-pig vas deferens.

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