Effects of hyperoxia and nitric oxide on endogenous nitric oxide production in polymorphonuclear leukocytes.

Background: Exposure to hyperoxia and nitric oxide (NO) occur frequently during the treatment of neonatal hypoxic pulmonary failure.

Objective: The aim of the study was to quantify the endogenous synthesis of NO in neonatal polymorphonuclear neutrophils following exposure to hyperoxia and NO in vitro.

Methods: Neonatal cord blood was exposed to room air, 25, 30 and 100% oxygen and 10 or 20 ppm NO added to the different oxygen concentrations for up to 30 min. 4,5-Diaminofluorescein diacetate (DAF-2 DA) is an intracellular dye used to measure real-time changes in NO levels in vivo. The molecular structure of DAF-2 DA changes upon contact with NO to its oxidized and fluorescent form diaminofluorescein-triazol (DAF-2T) and after being hydrolyzed by intracellular esterases cannot leave the cell. DAF-2 DA signals following equilibration with room air were used as controls.

Results: Exposure to 100% oxygen increased NO production significantly when compared to 20 ppm NO plus 100% oxygen (p = 0.031) and to 20 ppm NO alone (p = 0.006). 10 ppm NO produced a similar effect. Significant increases in NO production were also noticed following exposure to 25% oxygen. This increase was already present after 10 min of oxygen exposure.

Conclusion: These findings support the propagated avoidance of hyperoxia not only in preterm infants, but also in term neonates.