Oxygen tension and inhaled nitric oxide modulate pulmonary levels of S-nitrosocysteine and 3-nitrotyrosine in rats.

The oxidative environment within the lung generated upon administration of oxygen may be a critical regulator for the efficacy of inhaled nitric oxide therapy, possibly as a consequence of changes in nitrosative and nitrative chemistry. Changes in S-nitrosocysteine and 3-nitrotyrosine adducts were therefore evaluated after exposure of rats to 80% or >95% oxygen for 24 or 48 h with and without 20 ppm inhaled nitric oxide. Exposure to 80% oxygen led to increased formation of S-nitrosocysteine and 3-nitrotyrosine adducts in lung tissue that were also associated with increased expression of iNOS. The addition of inhaled nitric oxide in 80% oxygen exposure did not alter any of these adducts in the lung or in the bronchoalveolar lavage (BAL). Exposure to >95% oxygen led to a significant decrease in S-nitrosocysteine and an increase in 3-nitrotyrosine adducts in the lung. Co-administration of inhaled nitric oxide with >95% oxygen prevented the decrease in S-nitrosocysteine levels. The levels of S-nitrosocysteine and 3-nitrotyrosine returned to baseline in a time-dependent fashion after termination of exposure to >95% oxygen and inhaled nitric oxide. These data suggest the formation of S-nitrosating and tyrosine-nitrating species is regulated by oxygen tensions and co-administration of inhaled nitric oxide restores the nitrosative chemistry without a significant impact upon the nitrative pathway.