Effects of peroxide on endothelial nitric oxide synthase in coronary arteries

Reactive oxygen species (ROS) are produced in ischemia and reperfusion. Since endothelial nitric oxide synthase (eNOS) is key to the endothelium- dependent vasodilation, we examined the effects of peroxide on this enzyme. We treated cells cultured from pig coronary artery endothelium with different concentrations of hydrogen peroxide, washed them, solubilized them and measured NOS activity by arginine to citrulline conversion. Hydrogen peroxide inhibited the eNOS activity with an IC50 value of 0.85 ± 0.39 mM. In another experiment, we perfused arteries with solutions containing 0 or 1 mM hydrogen peroxide, washed them, removed the endothelium using a cotton swab, centrifuged and solubilized the endothelium and monitored its NOS activity. Hydrogen peroxide (1 mM) did not affect the NOS activity significantly (p > 0.05) in this assay. We conclude that the inactivation of eNOS by hydrogen peroxide does not play a major role in the ischemia- reperfusion damage because the peroxide concentrations attained during ischemia-perfusion are much lower than those affecting the eNOS activity.