Acute Hyperglycemia Attenuates Endothelium-Dependent Vasodilation in Humans In Vivo

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Abstract
Background —Endothelial function is impaired in patients with diabetes mellitus. However, the factors contributing to this defect are currently unknown. Hyperglycemia attenuates endothelium-dependent relaxation in normal rabbit arteries in vitro and rat arterioles in vivo. Accordingly, this study examined the effect of acute hyperglycemia on endothelium-dependent vasodilation in nondiabetic humans in vivo. Methods and Results —Endothelium-dependent vasodilation was assessed through brachial artery infusion of methacholine chloride both before and during 6 hours of local hyperglycemia (300 mg/dL) achieved by intra-arterial infusion of 50% dextrose. Forearm blood flow was determined by plethysmography. In a group of 10 subjects, there was a trend toward attenuated methacholine-mediated vasodilation during hyperglycemia compared with euglycemia ( P =.07 by ANOVA; maximal response, 13.3±2.8 versus 14.7±1.5 mL · min −1 · 100 mL −1 , respectively). In these subjects, the systemic serum insulin levels increased significantly during the dextrose infusion ( P <.001). To eliminate the confounding vasoactive effects of insulin, the protocol was repeated during systemic infusion of octreotide (30 ng · kg −1 · min −1 ) to inhibit pancreatic secretion of insulin. In these subjects (n=10), hyperglycemia significantly attenuated the forearm blood flow response to methacholine ( P <.01 by ANOVA; maximal response, 16.9±2.5 before versus 12.7±1.8 mL · min −1 · 100 mL −1 during hyperglycemia). Methacholine-mediated vasodilation was not attenuated by an equimolar infusion of mannitol ( P >.40), nor did hyperglycemia reduce endothelium-independent vasodilation to verapamil ( P >.50). Conclusions —Acute hyperglycemia impairs endothelium-dependent vasodilation in healthy humans in vivo. This finding suggests that elevated glucose may contribute to the endothelial dysfunction observed in patients with diabetes mellitus.