AN INHIBITORY EFFECT OF ETHANOL ON ADRENERGIC NEUROMUSCULAR TRANSMISSION IN THE GUINEA-PIG VAS DEFERENS

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Effects of ethanol on adrenergic neuromuscular transmission were investigated in the isolated vas deferens of the guinea-pig. The contractile responses to adrenergic nerve stimulation were depressed by ethanol in a concentration-dependent, reversible manner at a concentration range between 25 and 500 mM. Ethanol also depressed the contractions induced by exogenous noradrenaline. The resting membrane potentials recorded intracellularly from the smooth muscle cells were not affected by the alcohol. The excitatory junction potentials (EJPs) evoked by nerve stimulation decreased in amplitude, but the facilitation phenomena observed with repetitive stimulation remained unaltered. Ethanol slightly increased the frequency of the spontaneous EJPs, but decreased their amplitude. The extracellularly recorded action potentials from the small sympathetic nerve bundles innervating the vas deferens were suppressed by high concentrations of ethanol (more than 200 mM). These results indicate that ethanol inhibits adrenergic neuromuscular transmission in the vas deferens probably through depressing the sensitivity of the postsynaptic membrane to the transmitter and a block of axonal conduction in the presynaptic nerve terminals.
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