Chronic ethanol administration induces tolerance to morphine and to beta-endorphin responses in the rat vas deferens

The possibility was investigated that ethanol, chronically administered, might produce changes in the opioid receptors located on the sympathetic nerves of the rat vas deferens. Administration of ethanol, 3-9 g/kg per day for six days, resulted in tolerance to the hypnotic effects induced by ethanol (4 g/kg i.p.) and pentobarbital (35 mg/kg i.p.). Ethanol administration also resulted in tolerance to the effects of morphine and beta-endorphin on the muscular twitch evoked in the rat vas deferens by neuronal stimulation. In contrast, chronic ethanol did not significantly change the effects on vas deferens contractions induced by exogenous bioamines such as noradrenaline and dopamine and by acetylcholine. These results suggest that ethanol and opioids have certain biochemical mechanisms in common which might express themselves at the level of prejunctional components involved in the modulation of neurotransmitter action in the rat vas deferens.