Effects of inhaled nitric oxide or inhibition of endogenous nitric oxide formation on hyperoxic lung injury.

Nitric oxide (NO) may either protect against or contribute to oxidant-induced lung injury. In this study, we sought to determine whether either inhaled NO in concentration of 10 and 100 parts per million (ppm) or inhibition of endogenous NO formation with L-NG nitroarginine methyl ester (L-NAME) or aminoguanidine alters the extent of lung injury in rats breathing 100% O2. Lung thiobarbituric acid reactive substances (TBARS), wet to dry lung weight ratio (Q(W)/Q(D)), vascular and epithelial permeability (assessed by simultaneous intravenous administration of 131I-labeled albumin and intraalveolar instillation of 125I-labeled albumin), alveolar liquid clearance (evaluated based on the increase in alveolar protein concentration), and lung liquid clearance (gravimetric method) were determined after 40 h exposure to either 100% or 21% O2. Exposure to hyperoxia caused increases in lung TBARS from 10.5 +/- 0.7 to 13.7 +/- 1.5 micromol/mg protein (p < 0.05); in blood hemoglobin concentration (Hb) from 14 +/- 1 g/dl to 17 +/- 1 g/dl (p < 0.05); in the Q(W)/Q(D) ratio from 4.02 +/- 0.3 to 5.31 +/- 0.5 (p < 0.05); and in alveolar-arterial oxygen tension difference from 124 +/- 14 mm Hg to 241 +/- 61 mm Hg (p < 0.05); as well as a decrease in blood pressure, from 131 +/- 15 mm Hg to 72 +/- 26 mm Hg (p < 0.05). Hyperoxia also increased vascular albumin leakage and moderately altered epithelial barrier permeability to protein. Inhalation of 10 ppm NO prevented the increases in TBARS and Q(W)/Q(D), had no effect on the alveolar barrier impermeability to protein, and improved alveolar liquid clearance. Inhalation of 100 ppm NO did not alter the increases in TBARS and Q(W)/Q(D) but increased vascular permeability to protein. Survival of rats exposed to hyperoxia was not improved by inhaled NO. Treatment with L-NAME or aminoguanidine reduced survival. L-NAME, but not aminoguanidine, increased lung TBARs. These results suggest that, depending on its concentration, inhaled NO can either reduce or increase the early consequences of hyperoxic lung injury. Treatment with L-NAME, and to a lesser extent aminoguanidine, worsened hyperoxic lung injury, indicating a protective effect of endogenous NO.