Background: Pulmonary expression of heme oxygenase has been observed in multiple studies. This expression has been found beneficial in decreasing the severity of acute lung injury (ALI) post ischemia-reperfusion (I/R). The aim of this study was to assess the role of exogenous administration of the end-products of heme oxygenase reaction, carbon monoxide, and bilirubin, in the severity of ALI.
Study design: We compared five groups of rats (n = 7/group) including a sham group and four I/R of the lower extremities by clamping the abdominal aorta for 2 h followed by reperfusion for 2 h. The four I/R groups included a control group, one pretreated with bilirubin (50 micromol/kg IV), another with inhaled carbon monoxide (CO) (250 ppm), and the last pretreated with both. The severity of ALI has been evaluated by a histological assay grading neutrophilic infiltration, as well as a study of the microvascular permeability using the Evans blue.
Results: The administration of CO prevented pulmonary microvascular permeability alteration noted after I/R of the lower limbs (pulmonary content of Evans blue: 141 +/- 23 microg/g of tissue in the isolated I/R group versus 68 +/- 34 microg/g of tissue in CO group; P < 0.001). Histologically CO administration inhibited neutrophilic sequestration observed after I/R. On the other hand, treatment by bilirubin alone (50 micromol/kg IV) did not modify the extent of pulmonary injury.
Conclusion: Exogenous administration of carbon monoxide by inhalation at low doses prevented ALI post-I/R in this model.