Abstract：Objective To test intrinsic nitric oxide (NO) and endothelin (ET) activities in newborns with respiratory failure. Methods NO oxidation products (NO 2 -+NO 3 =NOx) and creatinine (Cr) were measured daily in the urine of 38 newborns with mechanical ventilation due to respiratory failure. NOx excretion was expressed by urine Cr excretion. Plasma ET was also tested in the patients. Lung compliance was monitored and oxygenation index (OI) was calculated in series. Results Five of the 38 patients developed respiratory distress syndrome. In these patients, urinary NOx (208.64±88.53 μmol/mg Cr) was extremely low while plasma ET was markedly high (82.36±17.83 ng/L). The average value of NOx (264.98±218.32 μmol/mg Cr) was significantly lower while plasma ET (73.01±10.06 ng/L) was higher in all the patients than those seen in the control newborns without pulmonary disease (397.26±206.61 μmol/mg Cr and 40.66±16.86 ng/L). Urinary NOx and plasma ET returned to the normal levels when the patients recovered from respiratory failure. In addition, the lower urinary NOx with the elevated plasma ET was related to the increased OI and to the reduced Lung Compliance. Conclusions Newborn patients with more severe respiratory failure have a lower level of urinary NO oxidation products and a higher level of plasma ET. The results suggest that the decrease of intrinsic NO production and the increase of ET induced by severe hypoxemia may play an important role in the pathogenesis of respiratory failure.
