Sodium nitroprusside mitigates oleic acid-induced acute lung injury

BACKGROUND: Acute lung injury (ALI) is associated with pulmonary hypertension, intrapulmonary shunting, and increased microvascular permeability, leading to altered oxygenation capacity. Oleic acid (OA) creates a significant ALI that physiologically mimics human adult respiratory distress syndrome (ARDS). It has been hypothesized that pulmonary vasodilatation may improve ALI. Studies in our laboratory using this model and nitric oxide (NO) have shown that NO inhalation is detrimental and worsens the effects of OA. We studied the effect of pretreatment with a potent vasodilator, sodium nitroprusside (SNP), on ALI induced by OA in an isolated lung model. We hypothesized that pretreatment with SNP will worsen pulmonary hypertension and oxygenation in OA-induced ALI, similar to the effects seen with inhaled NO in this model. METHODS: Rabbit heart lung blocks were isolated, flushed in vivo, harvested, immediately perfused with whole blood, and ventilated with 50% oxygen. Pulmonary artery pressure was determined every 15 seconds for 90 minutes of perfusion. Oxygenation was determined by blood gas analysis of pulmonary venous effluent at 0, 20, 40, 60, and 90 minutes after initiation of OA infusion. Four groups were studied: saline control (SC), oleic acid control (OAC; 20-minute infusion of 50% OA/ethanol into pulmonary circulation), SNP control (NPC; 10 microg/ kg/min SNP infused without subsequent OA infusion), and SNP treatment (NPRx); 10 microg/kg/min SNP infused before OA/ethanol. Pulmonary artery pressure (PAP), oxygenation (arterio-venous oxygen difference [AVO2], compliance (CPL), and wet/dry lung weight were determined. RESULTS: No significant differences were found between the NPRx group and SC. Pretreatment with SNP eliminated the detrimental effects of OA infusion. CONCLUSIONS: Contrary to our hypothesis, pretreatment with SNP eliminates the decrease in oxygenation and increase in lung weight, and ameliorates pulmonary hypertension in our isolated lung model of OA-induced ALI.