AN ELECTROPHARMACOLOGICAL ANALYSIS OF THE EFFECTS OF SOME DRUGS ON NEUROMUSCULAR TRANSMISSION IN THE VAS DEFERENS OF THE GUINEA-PIG

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Abstract
The effects of several drugs upon the excitatory junction potential (e.j.p.) in the guinea-pig vas deferens have been investigated. Amiodarone, a noradrenergic neuron blocker which also blocks both .alpha.- and .beta.-adrenoreceptors, did not reduce the e.j.p. 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. Sotalol, a .beta.-adrenoreceptor antagonist, was without effect upon the e.j.p. Clonidine and LSD, .alpha.-adrenoreceptor agonists, produced a dose dependent inhibition of the e.j.p. without apparently affecting the frequency or size of spontaneous junction potentials. The effects of clonidine were antagonized by piperoxan in a competitive reversible manner. Results apparently 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 [norepinephrine] or that the postjunctional receptors responsible for the generation of the e.j.p. are not adrenoreceptors.