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THE CONTRACTILE EFFECTS OF 5‐HYDROXYTRYPTAMINE ON THE RAT ISOLATED VAS DEFERENS
Author(s) -
HAY D.W.P.,
WADSWORTH R.M.
Publication year - 1982
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1982.tb09338.x
Subject(s) - methysergide , endocrinology , medicine , verapamil , nifedipine , reserpine , vas deferens , phentolamine , guanethidine , chemistry , contraction (grammar) , flunarizine , muscle contraction , calcium , serotonin , biology , receptor , stimulation
1 5‐Hydroxytryptamine (5‐HT) (5.16–1291 μ m ) produced a phasic contraction followed later by rhythmic contractions in the rat vas deferens, primarily in the epididymal half. 5‐HT (129 μ m ) produced no response in Ca 2+ ‐free solution. Nifedipine (0.29 μ m ) or verapamil (2.04 μ m ) inhibited the initial phasic response to 5‐HT, but inhibition of the rhythmic contractions required concentrations 5 fold (nifedipine) or 30 fold (verapamil) higher. 2 Methysergide (2.13 μ m ) abolished the phasic and reduced the frequency of the rhythmic contractions. Phentolamine (2.65 μ m ) did not affect the phasic response but reduced the amplitude of the rhythmic contractions. The combination of phentolamine (2.65 μ m ) and methysergide (2.13 μ m ) completely abolished the response to 5‐HT (129 μ m ). 3 Desipramine (1.32 μ m ) had no effect on the phasic response to 5‐HT (129 μ m ), but the rhythmic contractions were reduced in amplitude with no effect on their frequency. 4 In vasa deferentia removed from reserpine‐treated or from guanethidine‐denervated rats, both phasic and rhythmic components of the 5‐HT (129 μ m ) contraction were augmented due to supersensitivity. 5 It is concluded that the phasic component of the 5‐HT contraction is mediated by post‐junctional 5‐HT receptors, while the rhythmic component is mediated by the combination of post‐junctional 5‐HT receptors and noradrenaline released from neuronal stores. Assuming that nifedipine and verapamil are acting solely by inhibition of calcium channels, the phasic and rhythmic components of the 5‐HT response may be mediated through separate Ca 2+ channels. If this is correct, one channel might be a voltage‐dependent channel and the other could be similar to, but distinct from the channel mediating the response to methoxamine.