Ethanol-induced vasoconstriction is mediated via redox-sensitive cyclo-oxygenase-dependent mechanisms

The present study investigated the role of ROS (reactive oxygen species) and COX (cyclo-oxygenase) in ethanol-induced contraction and elevation of [Ca²⁺]_i (intracellular [Ca²⁺]). Vascular reactivity experiments, using standard muscle bath procedures, showed that ethanol (1–800 mmol/l) induced contraction in endothelium-intact (EC₅₀: 306±34 mmol/l) and endothelium -denuded (EC₅₀: 180±40 mmol/l) rat aortic rings. Endothelial removal enhanced ethanol-induced contraction. Preincubation of intact rings with L-NAME [N^G-nitro-L-arginine methyl ester; non-selective NOS (NO synthase) inhibitor, 100μmol/l], 7-nitroindazole [selective nNOS (neuronal NOS) inhibitor, 100μmol/l], oxyhaemoglobin (NO scavenger, 10μmol/l) and ODQ (selective inhibitor of guanylate cyclase enzyme, 1μmol/l) increased ethanol-induced contraction. Tiron [O₂⁻ (superoxide anion) scavenger, 1 mmol/l] and catalase (H₂O₂ scavenger, 300 units/ml) reduced ethanol-induced contraction to a similar extent in both endothelium-intact and denuded rings. Similarly, indomethacin (non-selective COX inhibitor, 10μmol/l), SC560 (selective COX-1 inhibitor, 1μmol/l), AH6809 [PGF_2α (prostaglandin F_2α)] receptor antagonist, 10μmol/l] or SQ29584 [PGH₂(prostaglandin H₂)/TXA₂ (thromboxane A₂) receptor antagonist, 3μmol/l] inhibited ethanol-induced contraction in aortic rings with and without intact endothelium. In cultured aortic VSMCs (vascular smooth muscle cells), ethanol stimulated generation of O₂⁻ and H₂O₂. Ethanol induced a transient increase in [Ca²⁺]_i, which was significantly inhibited in VSMCs pre-exposed to tiron or indomethacin. Our data suggest that ethanol induces vasoconstriction via redox-sensitive and COX-dependent pathways, probably through direct effects on ROS production and Ca²⁺ signalling. These findings identify putative molecular mechanisms whereby ethanol, at high concentrations, influences vascular reactivity. Whether similar phenomena occur in vivo at lower concentrations of ethanol remains unclear.