Effect of dietary vitamin E supplementation on vascular reactivity of thoracic aorta in streptozotocin-diabetic rats

The present study evaluated the effect of dietary vitamin E supplementation (1,000 mg/kg chow) on the alterations in vascular reactivity of streptozot ocin-diabetic aorta of Wistar rats, After 12 weeks of treatment, thoracic a ortic rings of rats were mounted in organ baths and contractile responses t o phenylephrine and 5-hydroxytryptamine and relaxant responses to acetylcho line, calcium ionophore and sodium nitroprusside were assessed. Plasma vita min E concentration as measured by HPLC was markedly decreased in diabetic rats and increased with dietary vitamin E supplementation. Induction of dia betes significantly impaired endothelium-dependent relaxations to acetylcho line and calcium ionophore in aortic rings, but did not change endothelium- independent relaxation to sodium nitroprusside. Vitamin E significantly imp roved the impaired endothelium-dependent relaxations, further it decreased the enhanced contractile response to phenylephrine and 5-hydroxytryptamine in diabetic rings. The mechanical denudation of endothelium or the chemical inhibition of endothelium-dependent relaxation with N-omega-nitro-L-argini ne methyl eater (100 mu mol/l) significantly increased phenylephrine contra ctility in control rings and the rings of diabetic rats treated with vitami n E; such a difference was not observed in diabetic rats fed with normal di et. Liver and lung malondialdehyde concentrations, as an index of lipid per oxidation, were increased in diabetic rats and significantly decreased with vitamin E supplementation. It is concluded that dietary supplementation of vitamin E improved endothelial dysfunction in insulin-dependent model of u ncontrolled diabetes, probably decreasing membranal lipid peroxidation. Cop yright (C) 2001 S. Karger AG, Basel.