Background: Despite it is recognized that high level of nitrotyrosine formation may play a role in acute lung injury (ALI), few studies have assessed protein nitration in ALI after meconium aspiration. This study was undertaken to observe the expression of inducible nitric oxide synthase (iNOS) and formation of nitrotyrosine in ALI after meconium aspiration and evaluate the contribution of iNOS and nitrotyrosine to tissue injury.

Methods: Sixteen healthy male Sprage-Dawley rats were divided randomly into control group and meconium group, which were administrated intratracheally 1 ml/kg saline or 20% human newborn meconium suspension respectively. The animals were sacrificed 24 hours after treatment. Bronchoalveolar lavage fluid (BALF) cell count, BALF protein, pulmonary myeloperoxidase (MPO) activity, malondialdehide (MDA), and nitrate/nitrite levels were measured. Western blot was used to determine the expression of pulmonary nitrotyrosine, a specific "footprint" of peroxynitrite and iNOS. Lung injury score was also evaluated.

Results: Compared with the control group, the rats in the meconium group showed an increase in cell count (mean±SD 4.04±1.01 vs 0.53±0.19×10⁶/ml, P<0.01), BALF protein (mean±SD 2.54±0.74 vs 0.67±0.26 mg/L, P<0.01), pulmonary MPO activity (mean±SD 1.49±0.22 vs 0.62±0.16 U/g wet lung, P<0.01), MDA level (mean±SD 3.30±0.85 vs 1.40±0.35 nmol/mg protein, P<0.01), nitrate/nitrite level (mean±SD 12.77±5.00 vs 4.89±1.32 µmol/mg protein, P<0.01), and lung injury score (9.88±1.36 vs 2.25±1.04, P<0.01). Western blot examination demonstrated increased expression of nitrotyrosine and iNOS in the meconium group (mean±SD 0.46±0.19 vs 0.11±0.08 and 1.49±0.60 vs 0.13±0.11, respectively, P<0.01).

Conclusions: Meconium causes increased expression of pulmonary iNOS, leading to over production of NO and nitrotyrosine, which may be of pathogenic importance in ALI after meconium aspiration.