Correlation between exhaled nitric oxide and plasma nitrate levels in healthy individuals

Nitric oxide (NO), a free radical and a highly reactive gas, is formed by c leavage of the guanido group on arginine. NO plays an important role in man y pathophysiological processes. There is a transient release of small amoun ts of NO by macrophages, from endothelium, platelets, the adrenal medulla a nd kidneys. Biological functions mediated by NO include vasodilatation, reg ulation of vascular tone, inhibition of platelet aggregation, mitochondrial respiration and neuronal transmission. NO has been determined in the exhal ed gases in normal humans as well as in exhaled gases and in plasma in vari ous disease states. It is less invasive and more convenient to estimate NO levels in exhaled gases than in blood samples. This study has been designed to compare and correlate NO levels in exhaled gases and plasma of healthy individuals. After approval by the Research Subjects Review Board at this i nstitution, and written consent 50 adult subjects were studied. Plasma nitr ate and Nitric oxide levels were measured. There was only a weak or no corr elation between NO in exhaled gases and plasma nitrate levels in all subjec ts when plotted as a single group (R-2 = 0.11 and P = 0.02) or when compare d as separate genders, (R-2 = 0.26 and P = 0.01 for females, and R-2 = 0.03 and P = 0.37 for males). Similarly no correlation was found in NO and nitr ate levels in healthy subjects on no medications (R-2 = 0.08 and P = 0.07). This study shows that the levels of nitric oxide in exhaled gases most lik ely represents local pulmonary physiological processes and may not represen t systemic nitric oxide production in healthy individuals.