An electropharmacological analyses of the effects of some drugs on neuromuscular transmission in the vas deferens of the guinea-pig.

1 The effects of several drugs upon the excitatory junction potential (e.j.p.) in the guinea-pig vas deferens have been investigated. 2 Amiodarone, a noradrenergic neurone blocker which also blocks both alpha and beta-adrenoreceptors, did not reduce the e.j.p. 3 The alpha-adrenoreceptor antagonists, azapetine, piperoxan and prazosin, only enhanced the e.j.p. irrespective of their relative potencies at alpha 1 and alpha 2-adrenoreceptors. 4 Sotalol, a beta-adrenoreceptor antagonist, was without effect upon the e.j.p. 5 Clonidine and lysergic acid diethylamide, alpha-adrenoreceptor agonists, produced a dose dependent inhibition of the e.j.p. without apparently affecting the frequency or size of spontaneous junction potentials. 6 The effects of clonidine were antagonized by piperoxan in a competitive reversible manner. 7 It is argued that these results confirm the presence of alpha-adrenoreceptors prejunctionally upon the sympathetic excitatory innervation of the vas deferens but that although an endogenous alpha-adrenoreceptor agonist is released by nerve stimulation either the transmitter that is responsible for the e.j.p. is not noradrenaline or that the postjunctional receptors responsible for the generation of the e.j.p. are not adrenoreceptors.