Improvement of endothelial function and insulin sensitivity with vitamin Cin patients with coronary spastic angina - Possible role of reactive oxygen species

OBJECTIVES This study was designed to examine the effect of antioxidant sup plementation on the endothelial function and insulin sensitivity in patient s with coronary spastic angina (CSA). BACKGROUND Insulin resistance may play a key role in coronary heart disease , and there is a possible link between acetylcholine-induced coronary vasoc onstriction and hyperinsulinemia in patients with CSA. Endothelial dysfunct ion is present in the systemic arteries in CSA patients, and reactive oxyge n species may cause inactivation of nitric oxide in these patients. METHODS We measured flow-mediated dilation of the brachial artery using ult rasound technique in 22 patients with CSA and 20 control subjects. We also evaluated glucose tolerance using a 75-g oral glucose tolerance test and in sulin sensitivity using steady-state plasma glucose (SSPG) methods in the s ame patients. RESULTS The incidence of impaired glucose tolerance was higher in the CSA g roup than in the control group. Vitamin C infusion augmented flow-mediated dilation and decreased SSPG levels in the CSA group (from 3.27 +/- 0.77% to 7.00 +/- 0.59% [p < 0.001 by analysis of variance (ANOVA)] and from 177.3 +/- 13.3 to 143.1 +/- 14.9 mg/dl [p = 0.047 by ANOVA], respectively) but no t in the control group (from 6.47 +/- 0.66% to 6.80 +/- 0.60% and from 119. 8 +/- 11.7 mg/dl to 118.1 +/- 11.3 mg/dl, respectively). The steady-state p lasma insulin levels were not affected by vitamin C infusion in either grou p. CONCLUSIONS Vitamin C improves both endothelial function and insulin sensit ivity in patients with CSA. Thus, reactive oxygen species and/or decreased nitric oxide bioactivity may play an important role in the genesis of both endothelial dysfunction and insulin resistance in patients with CSA. (J Am Coll Cardiol 2000;35:1860-6) (C) 2000 by the American College of Cardiology .