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EFFECTS OF DOPAMINE ON ADRENERGIC NEUROMUSCULAR TRANSMISSION IN THE GUINEA‐PIG VAS DEFERENS
Author(s) -
BELL G.
Publication year - 1980
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.1476-5381.1980.tb14565.x
Subject(s) - phentolamine , dopamine , vas deferens , endocrinology , stimulation , medicine , neuromuscular transmission , neurotransmitter , chemistry , excitatory postsynaptic potential , inhibitory postsynaptic potential , receptor
1 In the isolated vas deferens of the guinea‐pig, contractile responses to adrenergic nerve stimulation at 2 Hz were depressed by exogenous dopamine (5 μ m ) and this effect was abolished in the presence of phentolamine (0.3 μ m ), suggesting that it was due to an agonist action of dopamine on α‐adrenotors. 2 The depression by dopamine (5 μ m ) of contractile responses to nerve stimulation was correlated with reduction in amplitude of single excitatory junction potentials (e.j.ps) evoked by nerve stimulation, but not with depression of spontaneous junction potentials. 3 By contrast, during repetitive nerve stimulation at 1 Hz the depressant effect of dopamine on e.j.p. amplitude became less pronounced, due to the amount of facilitation being greater than that occurring under control conditions in the same cell. 4 The α‐adrenoceptor antagonist, phentolamine (10 μ m ), also increased the amount of facilitation during repetitive nerve stimulation. 5 In the presence of phentolamine (10 μ m ), the depressant effect of dopamine (5 μ m ) on single e.j.ps was abolished but its enhancing effect on facilitation was not reduced. 6 It is suggested that the enhancement of facilitation during repetitive stimulation by both dopamine and phentolamine is independent of their actions on presynaptic α‐adrenoceptors.