Sodium Nitrite Mitigates Ventilator-induced Lung Injury in Rats

Background: Nitrite (NO2-) is a physiologic source of nitric oxide and protects against ischemia-reperfusion injuries. We hypothesized that nitrite would be protective in a rat model of ventilator-induced lung injury and sought to determine if nitrite protection is mediated by enzymic catalytic reduction to nitric oxide. Methods: Rats were anesthetized and mechanically ventilated. Group 1 had low tidal volume ventilation (LVT) (6 ml/kg and 2 cm H2O positive end-expiratory pressure; n = 10); group 2 had high tidal volume ventilation(HVT) (2h of 35 cm H2O inspiratory peak pressure and 0 cm H2O positive end-expiratory pressure; n = 14); groups 3-5: HVT with sodium nitrite (NaNO2) pretreatment (0.25, 2.5, 25 mu mol/kg IV; n = 6-8); group 6: HVT + NaNO2 + nitric oxide scavenger 2-(4-carboxyphenyl)-4,5dihydro-4,4,5,5-tetramethyl-1H-imidazolyl-1-oxy-3oxide (n = 6); group 7: HVT + NaNO2 + nitric oxide synthase inhibitor N-omega-nitro-L-arginine methyl ester (n = 7); and group 8: HVT + NaNO2 + xanthine oxidoreductase inhibitor allopurinol (n = 6). Injury assessment included physiologic measurements (gas exchange, lung compliance, lung edema formation, vascular perfusion pressures) with histologic and biochemical correlates of lung injury and protection. Results: Injurious ventilation caused statistically significant injury in untreated animals. NaNO2 pretreatment mitigated the gas exchange deterioration, lung edema formation, and histologic injury with maximal protection at 2.5 mu mol/kg. Decreasing nitric oxide bioavailability by nitric oxide scavenging, nitric oxide synthase inhibition, or xanthine oxidoreductase inhibition abolished the protection by NaNO2. Conclusions: Nitrite confers protection against ventilator-induced lung injury in rats. Catalytic reduction to nitric oxide and mitigation of ventilator-induced lung injury is dependent on both xanthine oxidoreductase and nitric oxide synthases.