The endothelium-dependent relaxation of rabbit aorta: effects of antioxidants and hydroxylated eicosatetraenoic acids.

Acetylcholine (ACh) induced concentration-dependent relaxations of rabbit aortic strips precontracted with noradrenaline. The relaxations were abolished if the endothelium of the strips was disrupted. Three different antioxidants (butylated hydroxytoluene, dithiothreitol and alpha-tocopherol) reversed the endothelium-dependent vasodilation in a concentration-dependent manner. However, the antioxidant ascorbic acid did not alter the vasodilatation. The hydroxylated eicosatetraenoic acids 5-HETE, 12-HETE, 15-HETE and 5,12-diHETE had no effect on aortic strips under basal or induced tension. These results suggest, that (non-cyclo-oxygenase) oxidation processes, insensitive to the action of ascorbic acid, represent a crucial step in the endothelium-dependent dilatation of rabbit aorta by ACh. The hydroxylated fatty acids tested are unlikely to mediate this relaxation.