[Vasodilating effect and its mechanism of ethanol on isolated rat thoracic aorta at different resting tension]

To investigate the vasodilating effect and its mechanism of ethanol on isolated rat thoracic aorta at different resting tension.The tension of the isolated Sprague-Dawley rat thoracic aorta rings perfused with different concentrations of ethanol was measured using organ bath technique.At different resting tension (1.0, 1.5, 2.0, 2.5, 3.0, 3.5 and 4.0 g), ethanol (0.1-7.0 per thousand) caused a concentration-dependent relaxation on endothelium-denuded aortic rings precontracted with KCl (6 x 10(-2)mol/L) or phenylephrine (PE, 10(-6) mol/L), and the vasodilating effect was the most potent when the aortic rings were at the resting tension of 3 g. Ethanol had much less vasodilating effect on endothelium-intact aortic rings. Ethanol at 3 per thousand (the maximum-effect concentration) inhibited the CaCl2 induced contraction and downward shifted concentration-response curve of endothelium-denuded aortic rings pre-contracted with KCI or PE at the resting tension of 3 g. Incubation of aorta with ruthenium red (10(-5) mol/L) or heparin (50 mg/L) decreased the vasodilating effect of ethanol (3.0 per thousand) on endothelium-denuded aorta precontracted with PE at the resting tension of 3 g.Ethanol induces endothelium-independent relaxation on rat thoracic aorta, which is concerned with the resting tension. This effect of ethanol may be mediated by the inhibition of voltage-dependent and receptor-operated Ca2+ channels in the vascular smooth muscle cells. The inhibition of the ryanodine receptor and trisphosphate inositol (IP3) pathway may also contribute to this effect.