We investigated the mechanisms involved in the enhancement of endothelin (ET)-1 vascular reactivity induced by ethanol consumption. Ethanol intake for 2, 6, and 10 weeks enhanced the ET-1-induced contractile response of endothelium-intact but not endothelium-denuded rat carotid rings independently of the treatment duration. Conversely, phenylephrine-induced contraction was not affected by ethanol intake. The contraction induced by IRL1620 ,Ala 11,15 )-ET-1-(8 -21)], a selective ET B agonist, was increased after treatment with ethanol in endothelium-intact but not in endothelium-denuded carotid rings. Moreover, ET-1-and IRL1620-induced relaxation was reduced in endothelium-intact phenylephrine-precontracted rings from ethanol-treated rats. Acetylcholine-induced relaxation was not affected by ethanol treatment. N G -Nitro-Larginine methyl ester, 1H-[1,2,4]-oxadiazolo[4,3-a]quinoxalin-1-one, indomethacin, and tetraethylammonium reduced the relaxation induced by IRL1620 in carotid glands from control but not ethanol-treated rats. The mRNA levels for ET A and ET B receptors were not altered by ethanol consumption. However, ethanol treatment reduced the protein expression of ET B receptors. Furthermore, immunohistochemical assays showed reduced immunostaining for endothelial ET B receptors after treatment with ethanol. We conclude that ethanol consumption enhances ET-1-induced contraction in the rat carotid and that this response is not different among the three periods of treatment used in this study. Finally, the potentiation of ET-1-induced vascular reactivity is probably caused by reduced expression of relaxing endothelial ET B receptors.