title: Direct and indirect contractile responses of the human vas deferens and actions of noradrenaline and of calcium antagonists.
abstract: 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.
authors.affiliation: Division of Biomedical Sciences, King's College London, University of London.
authors.forename: I C
authors.initials: IC
authors.lastname: Smith
authors.forename: M
authors.initials: M
authors.lastname: Bray
mesh_terms: D002118:Calcium / Q000502:physiology; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D004558:Electric Stimulation; D006801:Humans; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009543:Nifedipine / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology*; D011224:Prazosin / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology; D014649:Vas Deferens / Q000187:drug effects* / Q000294:innervation / Q000502:physiology; D014700:Verapamil / Q000494:pharmacology
chemical_list: D002121:Calcium Channel Blockers; D013779:Tetrodotoxin; D014700:Verapamil; D009543:Nifedipine; D002118:Calcium; D009638:Norepinephrine; D011224:Prazosin