Effects of simulated hyperglycemia, insulin, and glucagon on endothelial nitric oxide synthase expression

Diabetes is associated with endothelial dysfunction and increased risk of h ypertension, cardiovascular disease, and renal complications. Earlier studi es have revealed that hyperglycemia impairs nitric oxide (NO) production an d diabetes causes endothelial dysfunction in humans and experimental animal s. This study was designed to test the effects of altered concentrations of glucose, insulin, and glucagon, the principal variables in types I and II diabetes, on NO production and endothelial NO synthase (eNOS) expression in cultured human coronary endothelial cells. Cultured endothelial cells were incubated in the presence of glucose at either normal (5.6 mM) or high (25 mM) concentrations for 7 days. The rates of basal and bradykinin-stimulate d NO production (nitrate + nitrite) and eNOS protein expression (Western bl ot) were then determined at the basal condition and in the presence of insu lin (10(-8) and 10(-7) M), glucagon (10(-8) and 10(-7) M), or both. Incubat ion with a high-glucose concentration for 7 days significantly downregulate d, whereas insulin significantly upregulated, basal and bradykinin-stimulat ed NO production and eNOS expression in cultured endothelial cells. The sti mulatory action of insulin was mitigated by high-glucose concentration and abolished by cotreatment of cells with glucagon. Thus hyperglycemia, insuli nopenia, and hyperglucagonemia, which frequently coexist in diabetes, can w ork in concert to suppress NO production by human coronary artery endotheli al cells.