Direct and indirect contractile responses of the human vas deferens and actions of noradrenaline and of calcium antagonists

Contractile responses of the isolated human vas deferens, obtained from vasectomy operations, were measured. Large single electrical shocks gave a twitch response with short latency (0.36 s) which was insensitive to prazosin (5 microM) or TTX (0.2 microM) and was thus identified as due to direct muscle stimulation. A train of 100 low intensity shocks gave a response with a longer latency (1.9 s) which was substantially sensitive to both prazosin and TTX; we assume this response is dominated by an indirect nerve-induced contraction. Relaxations, presumably caused by activation of circular muscle, were recorded from regions of some preparations both by direct and indirect stimulation. Noradrenaline (10-20 microM) induced a tonic contracture, spontaneous contractions and a large potentiation of the response to direct stimulation--but not to indirect stimulation implying a strong presynaptic inhibition. Noradrenaline also speeded the relaxation from contractions. Verapamil (1-100 microM) and nifedipine had no effect on the direct responses but verapamil (10 microM) inhibited the indirect response. Calcium removal prevented most, and 5 mM-EDTA all, of the direct response. However, even with EDTA, noradrenaline was able to support spontaneous and stimulus-induced contractions. Thus contraction of the vas, though sustained by external calcium, does not appear to directly depend on it.