17-Estradiol Antagonizes the Down-Regulation of Endothelial Nitric-Oxide Synthase and GTP Cyclohydrolase I by High Glucose: Relevance to Postmenopausal Diabetic Cardiovascular Disease

In postmenopausal women, the risk of diabetic cardiovascular disease drastically increases compared with that of men or premenopausal women. However, the mechanism of this phe-nomenon has not yet been clarified. We hypothesized that the beneficial effects of estrogen on endothelial function may be relevant to protection against hyperglycemia-induced vascular derangement. Bovine aortic endothelial cells were incubated for 72 h in the presence and absence of the physiological concentration of 17-estradiol (17-E2) under normal and high-glucose conditions. The presence of 17-E2 significantly coun-teracted the reduction in basal nitric oxide production under high-glucose conditions. This finding was associated with the recovery of endothelial nitric-oxide synthase (eNOS) protein expression, tetrahydrobiopterin (BH4) levels, and the activit