Background Hyperglycemia is a primary cause of premature vascular disease. Endothelial cell dysfunction characterized by diminished endothelium-dependent relaxations is likely to be involved. Little is known about the molecular mechanisms of hyperglycemia-induced endothelial dysfunction.

Methods and Results This study was designed to determine the effect of hyperglycemia on the l-arginine/nitric oxide (NO) pathway. Expression of endothelial nitric oxide synthase (eNOS) mRNA and production of NO were studied in human aortic endothelial cells exposed to control levels (5.5 mmol/L) and high levels (22.2 mmol/L) of glucose for 5 days. We examined the effect of glucose on NO release by measuring changes in nitrite (NO₂⁻) levels by Griess reaction. Superoxide anion (O₂⁻) production was also examined by the ferrocytochrome c assay. NOS mRNA and protein expression, which were evaluated by reverse transcription–polymerase chain reaction and Western blotting, were approximately twofold greater in endothelial cells exposed to high glucose. Elevated glucose levels increased NO₂⁻ production by only 40% but increased the release of O₂⁻ by more than threefold.

Conclusions The present study demonstrates that prolonged exposure to high glucose increases eNOS gene expression, protein expression, and NO release. However, upregulation of eNOS and NO release is associated with a marked concomitant increase of O₂⁻ production. These results provide the molecular basis for understanding how chronic exposure to elevated glucose leads to an imbalance between NO and O₂⁻. This may explain impaired endothelial function and be important for diabetic vascular disease.