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

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

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.

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.

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.

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