Plasma arginine levels and the response to inhaled nitric oxide in neonates

Inhaled nitric oxide (iNO) can be an effective vasodilator in pulmonary hyp ertension of the newborn (PHN). The aim of this study was to determine whet her differences in arginine levels, from which endogenous NO is produced, e xplain the variability in response to NO and whether the arginine levels we re lower in term and preterm infants with PHN than in infants without PHN ( controls). We prospectively studied 30 infants (17 born preterm) with clini cally diagnosed PHN and treated with iNO and 22 controls (14 born preterm). Three NO levels (10, 20, 40 ppm) were administered to the PHN infants to i dentify that associated with maximum oxygenation. Twenty-seven infants with PHN improved following iNO and had lower arginine levels than those infant s who did not respond to iNO (p < 0.05). No significant relationship, howev er, was noted between the arginine levels and either the magnitude of chang e in the oxygenation index in response to iNO or the NO level associated wi th maximum oxygenation. The median plasma arginine level prior to iNO of th e PHN infants was 12.5 (range 2-53) mu mol/l, but not significantly lower t han that of the controls (median 24, range 3-82 mu mol/l). We conclude that differences in plasma arginine levels are unlikely to explain the variatio n in response to iNO and that, although arginine levels tended to be lower in infants with PHN, this is not a consistent finding in either the term or preterm infants. Copyright (C) 1999 S. Karger AG,Basel.