Alcohol interactions with brain opiate receptors.

Ethanol, added in vitro to mouse caudate membranes, inhibited high-affinity binding of 0.2 nM 3H-dihydromorphine (3H-DHM) over an ethanol concentration range of 250-1,000 mM. At lower, physiologically-attainable ethanol concentrations (e.g.: 50 mM), 3H-DHM binding was significantly increased. Over the concentration range of 50-1,000 mM, ethanol inhibited 0.5 nM 3H-[D-Ala2,D-Leu5]enkephalin (3H-ENK) binding to mouse caudate tissue, and no stimulation of 3H-ENK binding was noted at any of these concentrations of ethanol. Ethanol inhibits opiate binding in a pseudo-competitive manner and, therefore, the concentration of ligand used to assess the effects of ethanol is of major importance. Results obtained with other alcohols which differ in their membrane:water partition coefficients suggest that alcohol effects on opiate binding are not solely dependent on the membrane-disordering properties of the alcohols.