Dietary antioxidant supplementation reduces lipid peroxidation but impairs vascular function in small mesenteric arteries of the streptozotocin-diabetic rat

Impaired endothelium-dependent relaxation could underlie many of the vascular complications associated with insulin-dependent diabetes mellitus, and may be mediated by increased oxidative stress. The effect of antioxidants on vascular endothelial function and oxidative stress of streptozotocin-diabetic rats was assessed by dietary supplementation with vitamins E and C. Diabetic (i.v. streptozotocin, 45 mg/kg) male Sprague-Dawley rats were fed one elf six supplemented diets containing 75.9, 250, or 500 mg vitamin E/kg chow, 250 mg vitamin C/kg H2O, 250 mg vitamin E/kg chow plus 250 mg Vitamin C/kg H2O, or chow deficient in vitamin E, and then compared to standard-fed control rats. After 4 weeks, small mesenteric arteries were dissected and mounted on a small vessel myograph, concentration response cut-yes were then constructed to noradrenaline, acetylcholine and sodium nitroprusside. Acetylcholine-mediated relaxation was impaired iii arteries from diabetic rats (pEC(50) 6.701 +/- SEM 0.120, n = 8) compared to controls (7.386 +/- 0.078, n = 6; p < 0.05). The 500 mg/kg vitamin E diet further impaired maximum relaxation to acetylcholine (58.2 +/- 10.5 vitamin E, n = 7 vs 84.4 +/- 5.3 % standard,p < 0.05), and the combined vitamin E plus C diet impaired maximum relaxation to sodium nitroprusside (48.5 +/- 4.1 in vitamin E + C, n = 8 vs 75.6 +/- 3.9 % standard; p < 0.01). However, plasma 8-epi-prostaglandin (PG)F-2 alpha (measured as an estimate of oxidative stress) was dose-dependently decreased in rats on vitamin E supplemented diets. Dietary antioxidant supplementation did not reverse impaired endothelial function in this model of uncontrolled diabetes despite a concomitant decrease in oxidative stress.