Endothelin Contributes to Basal Vascular Tone and Endothelial Dysfunction in Human Obesity and Type 2 Diabetes
- 1Division of Endocrinology & Metabolism, Indiana University-Purdue University Indianapolis School of Medicine, Indianapolis, Indiana
- 2Amylin Pharmaceuticals, Indianapolis, Indiana
Endothelium-dependent vasodilation is impaired in clinical states of insulin resistance such as obesity and type 2 diabetes. Individuals who have hyperinsulinemic insulin resistance have relatively elevated circulating levels of endothelin (ET)-1, suggesting that ET-1 may be important in the endothelial dysfunction and alterations of vascular tone in these conditions. In 8 lean subjects, 12 nondiabetic obese subjects, and 8 subjects with type 2 diabetes, we measured basal and methacholine-stimulated rates of leg blood flow (LBF) and total serum nitrates (NOx) before and after the intrafemoral arterial administration of BQ123, a specific blocker of ETA receptors. BQ123 produced significant vasodilation in the obese and type 2 diabetic subjects (leg vascular resistance = mean arterial pressure/LBF fell by 34 and 36%; P < 0.005) but not in the lean subjects (13%; P = NS, P = 0.018 comparing all groups). ETA blockade did not change basal NOx flux (NOx*LBF). This suggests increased basal ET-1 constrictor tone among obese and type 2 diabetic subjects. BQ123 corrected the baseline defect in endothelium-dependent vasodilation seen in obese and type 2 diabetic subjects, suggesting an important contribution of ET-1 to endothelial dysfunction in these subjects. In contrast to basal conditions, stimulated NOx flux was augmented by BQ123 in obese and type 2 diabetic subjects but not in L subjects (P = 0.04), suggesting a combined effect of ETA blockade to reduce constrictor tone and augment dilator tone. Endothelin seems to contribute to endothelial dysfunction and the regulation of vascular tone in human obesity and type 2 diabetes.
Address correspondence and reprint requests to Kieren Mather, MD, Division of Endocrinology & Metabolism, Department of Medicine, Indiana University School of Medicine, CL459, 541 North Clinical Dr., Indianapolis, IN 46202. E-mail:.
Received for publication 27 November 2001 and accepted in revised form 26 August 2002.
ET, endothelin; HOMA-IR, homeostasis model assessment-insulin resistance; LBF, leg blood flow; LVR, leg vascular resistance; MAP mean arterial pressure; NO nitric oxide; NOx, total nitrate.