OBJECTIVETo evaluate effects of inhaled nitric oxide (iNO) on the expression of lung neutrophil adhesion molecule CD(11b) in experimental meconium aspiration pneumonia treated with conventional mechanical ventilation under room air or 100% O(2).

METHODSRabbits were randomly allocated to 10 groups (n = 60), 6 of each group. Control or meconium aspiration pneumonia model groups were inhaled with room air or 100% O(2). Six treatment groups were treated with continuous NO inhalation at the doses of 6 x 10(-6), 10 x 10(-6) and 20 x 10(-6), respectively for 12 hours under room air or 100% O(2). The ratio of wet/dry (W/D) lung weight, alveolar septal width (ASW), myeloperoxidase (MPO) activity and lung injury score were measured. The expression of CD(11b) in neutrophils of the bronchoalveolar lavage fluid (BALF) was detected with flow cytometry.

RESULTSAfter 12 hours ventilation, the oxygenation was maintained better in treatment groups under different O(2) concentrations than that in model groups. Inflammatory evidence was found in lungs from all the model groups and treatment groups, which was characterized by serious inflammatory cell infiltration in alveolar space and hyaline membrane formation. The lung inflammation was decreased in all groups with nitric oxide inhalation. The ratio of W/D lung weight and ASW among different groups had no significant difference. MPO activities were significantly decreased in groups treated with 10 x 10(-6) and 20 x 10(-6) iNO compared with the model groups [with the concentration of 21% O(2), (1.8 +/- 0.2) U/g vs (4.4 +/- 0.5) U/g and (2.0 +/- 0.1) U/g vs (4.4 +/- 0.5) U/g;with the concentration of 100% O(2), (1.7 +/- 0.4) U/g vs (2.8 +/- 0.5) U/g and (1.4 +/- 0.3) U/g vs (2.8 +/- 0.5) U/g, P < 0.05, respectively]. MPO activities in the 20 x 10(-6) iNO group under 100% O(2) were significantly reduced compared with those under 21%O(2) [(1.4 +/- 0.3) U/g vs (2.0 +/- 0.1) U/g, P < 0.05]. Nitric oxide inhalation with the doses of 10 x 10(-6) and 20 x 10(-6) significantly decreased the expression of CD(11b) (MFI) in neutrophils of the BALF compared with the expressions in model groups without NO treatment (with 21% O(2), 121 +/- 20 vs 392 +/- 204 and 112 +/- 30 vs 392 +/- 204; with 100% O(2), 113 +/- 24 vs 293 +/- 65 and 102 +/- 14 vs 293 +/- 65, P < 0.05, respectively). Under the same iNO dose (10 x 10(-6) or 20 x 10(-6)) no statistic difference was found between groups of different inspired oxygen concentrations (21% and 100%).

CONCLUSIONSInhaled nitric oxide with the doses of 10 x 10(-6) to 20 x 10(-6) could significantly down-regulate the CD(11b) expression in neutrophil of the BALF and reduce the neutrophil sequestration and MPO activity in rabbit lungs, which may decrease the lung inflammation process in meconium aspiration pneumonia.