The role of endothelial nitric oxide synthase coupling status during acute hyperglycemia as determined by real‐time measurements of blood nitric oxide and hydrogen peroxide in rat (832.2)

Abstract

Acute hyperglycemia impairs vascular dilatory function in normal subjects. Normally, vascular endothelial function depends on nitric oxide (NO) production from coupled eNOS in the presence of cofactor 5,6,7,8‐tetrahydrobiopterin (BH4). By contrast, 7,8‐dihydrobiopterin (BH2, oxidized form of BH4) and/or lack of L‐arginine (eNOS substrate) causes eNOS uncoupling to produce superoxide (SO), which can be quickly converted to hydrogen peroxide (H2O2). The role of eNOS coupling status in mediating acute hyperglycemia‐induced vascular dysfunction is not known. We simultaneously measured blood NO and H2O2 during the infusion of saline (control), or 20% glucose with or without BH4 (MW=314 g/mol, 6.5 mg/kg), or L‐arginine (MW=211 g/mol, 600 mg/kg), or BH2 (MW=239 g/mol, 4 mg/kg) by NO or H2O2 microsensors (100 µm, WPI Inc.) from the femoral veins of male Sprague‐Dawley rats. We found that acute hyperglycemia (200 mg/dL, n=6) significantly increased blood H2O2 and reduced blood NO levels compared to the saline group over a 3 hr. period (n=7, p<0.05). By contrast, BH4 (n=6), or L‐arginine (n=5‐6), not BH2 (n=6‐7), significantly reduced blood H2O2 and improved vascular NO levels (p<0.05). This study provides novel evidence indicating that eNOS uncoupling during acute hyperglycemia causes endothelial dysfunction and oxidative stress. Promotion of eNOS coupling may be beneficial to maintain normal vascular function. Grant Funding Source: Supported by Center for Chronic Disorders of Aging and Department of Bio‐Medical Sciences at PCOM