ASSESSMENT OF ENDOGENOUS NITRIC-OXIDE FORMATION IN NEWBORNS - MEASUREMENT OF URINARY NITRITE AND NITRATE CONCENTRATIONS

We measured the urinary nitrite and nitrate (NOx-) excretion, an index of endogenous nitric oxide formation, in term and preterm newborns on the ist and 4th days of age. In the infants of both groups, the urina ry NOx- excretion significantly increased from the ist to the 4th day. The urinary NOx- excretion in preterm infants was significantly highe r as compared with term babies on both days. Furthermore, the urinary NOx- excretion was significantly elevated in preterm infants with resp iratory distress syndrome as compared with those without cardiopulmona ry complications on the 4th day. These changes of urinary NOx- excreti on in newborns strongly suggest the presence of an active physiologica l role for nitric oxide in the circulatory adaptation to extrauterine life.