OBJECTIVETo investigate possible role of carbon monoxide (CO) and heme oxygenase (HO) in the pathogenesis of acute respiratory distress syndrome (ARDS) induced by oleic acid (OA) and to compared with that induced by nitric oxide (NO).

METHODSARDS model was established in rats by oleic acid injection and concentrations of CO and NO in pulmonary arterial, carotid jugular blood and bronchoalveolar lavage fluid (BALF) were measured sequentially. Immunohistochemical method was used to determine the expression of HO in the lung.

RESULTSPulmonary arterial pressure in ARDS rats elevated 10 min after OA injection [(13.80 +/- 1.87) mm Hg to (19.51 +/- 5.02) mm Hg]. At 0.5 h after OA injection, concentration of CO in pulmonary artery began to increase and was markedly higher at 2 h than that in control rats [(0.135 +/- 0.010) g/L versus (0.116 +/- 0.005) g/L] (P < 0.01), also higher than that in carotid artery [(0.117 +/- 0.013) g/L] and in jugular vein [(0.107 +/- 0.018) g/L] in the same group, and maintained at a relatively high level thereafter. Concentration of CO in BALF also increased at 0.5 - 24 h and diminished at 72 h, as compared with that in controls. Concentration of NO in blood of pulmonary and systemic circulation all elevated markedly at 0.5 h and 2 h after OA injection, and then declined to normal at 12 h. Concentration of NO in BALF was significantly higher than that in controls. Arterial blood gas analysis showed that PaO2 markedly decreased in ARDS rats, especially at 2 h after OA injection. HO-2 could be expressed in the lung tissues of normal rats with immunohistochemical method, the strongest in epithelial cells of the bronchi, and HO-1 could only be expressed in pulmonary blood vessel walls, bronchial epithelial cells, alveolar epithelial cells and inflammatory cells of ARDS rats, lasting for 72 h after OA injection, consistent with that of CO level.

CONCLUSIONARDS rats showed a lastecl increase of CO level in pulmonary blood circulation, suggesting CO/HO system might play a more important role in modulation of blood vessel tension than NO might do in pathogenesis of ARDS.