Assessment of Endogenous Nitric Oxide Formation in the Neonate : Measurement of Urinary Nitrite and Citrulline Concentrations

ABSTRACT

PURPOSE: At birth, as the fetus adjusts to the "new world", the fetal pulmonary circulation undergoes a striking transition, characterized by an immediate rise in pulmonary blood flow and a sustained decrease in pulmonary vascular resistance(PVR). In the factors which reduce PVR after birth, are ventilation of the lung by gas, increase of oxygen tension in pulmonary vascular system, and some vasoactive mediators. Nitric oxide(NO) is regarded as one of the vasoactive mediators. Therefore we attempted to determine endogenous NO formation in newborns by measuring urinary nitrite(NO2) and citrulline which are indexes of endogenous NO formation. METHODS: We measured the urinary excretion of NO2 and citrulline in 20 term and 15 preterm neonates at the age of 1, 3, 7 days. RESULTS: The urinary excretion of NO2 and citrulline in the neonate group was higher as compared with the older children group(P<0.05). And it increased from the 1st to the 3rd day in the neonatal period(P<0.05). Furthermore the urinary excretion of them and the gestational age were inversely related(P<0.05). CONCLUSION: These changes of the urinary excretion of NO2 and citrulline in the neonate group suggest the presence of an active physiological role of NO in the pulmonary vascular biology during neonatal transition.