VITAMIN-C IMPROVES ENDOTHELIUM-DEPENDENT VASODILATION IN PATIENTS WITH INSULIN-DEPENDENT DIABETES-MELLITUS

Objectives. We sought to determine whether the antioxidant vitamin C i mproves endothelium-dependent vasodilation of forearm resistance vesse ls in patients with insulin-dependent diabetes mellitus. Background En dothelium dependent vasodilation is impaired in patients with diabetes mellitus. Oxidatively mediated degradation of endothelium-derived nit ric oxide contributes to abnormal endothelium-dependent vasodilation i n animal models of diabetes mellitus. Methods. The study group include d 10 patients with insulin-dependent diabetes mellitus and 10 age-matc hed control subjects. Forearm blood flow was determined by venous occl usion plethysmography, Endothelium-dependent vasodilation was assessed by intraarterial infusion of methacholine (0.3 to 10 mu g/min). Endot helium-independent vasodilation was assessed by intraarterial infusion of nitroprusside (0.3 to 10 mu g/min). Forearm blood flow dose-respon se curves were determined for each drug infusion before and during con comitant infusion of vitamin C (24 mg/min). Results. In diabetic subje cts, endothelium-dependent vasodilation was augmented by the concomita nt infusion of vitamin C (p = 0.001). Endothelium-independent vasodila tion was not affected by the concomitant infusion of vitamin C (p = NS ). In control subjects, vitamin C infusion did not affect endothelium dependent vasodilation (p = NS). Conclusions. Vitamin C selectively re stores the impaired endothelium-dependent vasodilation in the forearm resistance vessels of patients with insulin-dependent diabetes mellitu s. These findings indicate that nitric oxide degradation by oxygen-der ived free radicals contributes to abnormal vascular reactivity in huma ns with insulin-dependent diabetes mellitus. (C) 1998 by the American College of Cardiology.