Diabetes
Vitamin C improves endothelium-dependent vasodilation in patients with
non-insulin-dependent diabetes mellitus.
Ting HH; Timimi FK; Boles KS; Creager SJ; Ganz P; Creager MA
J Clin Invest 1996 Jan 1;97(1):22-8
Endothelium-dependent vasodilation is impaired in humans with diabetes
mellitus. Inactivation of endothelium-derived nitric oxide by oxygen-derived
free radicals contributes to abnormal vascular reactivity in experimental
models of diabetes. To determine whether this observation is relevant
to humans, we tested the hypothesis that the antioxidant, vitamin C, could
improve endothelium-dependent vasodilation in forearm resistance vessels
of patients with non-insulin-dependent diabetes mellitus. We studied 10
diabetic subjects and 10 age-matched, nondiabetic control subjects. Forearm
blood flow was determined by venous occlusion plethysmography. Endothelium-dependent
vasodilation was assessed by intraarterial infusion of methacholine (0.3-10
micrograms/min). Endothelium-independent vasodilation was measured by
intraarterial infusion of nitroprusside (0.3-10 micrograms/min) and verapamil
(10-300 micrograms/min). Forearm blood flow dose-response curves were
determined for each drug before and during concomitant intraarterial administration
of vitamin C (24 mg/min). In diabetic subjects, endothelium-dependent
vasodilation to methacholine was augmented by simultaneous infusion of
vitamin C (P = 0.002); in contrast, endothelium-independent vasodilation
to nitroprusside and to verapamil were not affected by concomitant infusion
of vitamin C (P = 0.9 and P = 0.4, respectively). In nondiabetic subjects,
vitamin C administration did not alter endothelium-dependent vasodilation
(P = 0.8). We conclude that endothelial dysfunction in forearm resistance
vessels of patients with non-insulin-dependent diabetes mellitus can be
improved by administration of the antioxidant, vitamin C. These findings
support the hypothesis that nitric oxide inactivation by oxygen-derived
free radicals contributes to abnormal vascular reactivity in diabetes.
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