Endothelial and inducible nitric oxide synthase gene and protein expression in hyperoxia-induced lung injury in premature rat
AIM: In a preterm rat model of hyperoxia-induced lung injury, we studied the effect of prolonged (7 d) hyperoxia on endothelial nitric oxide synthase (eNOS) and inducible nitric oxide synthase (iNOS) expression in the lungs. METHODS: Preterm rats were delivered by hysterotomy at 21 d gestation and randomly divided into hyperoxia group and room-air control and continuous exposure to oxygen (oxygen >0.95) or room air during 7 d. The animals were sacrificed on d 7 of life with an overdose of intraperitoneal pentobarbital. The mRNA levels of the eNOS, iNOS were measured by reverse-transcription polymerase chain reaction (RT-PCR). eNOS and iNOS protein expression measured by Western blotting. In addition, lung wet/dry weight ratio, the protein and cellular content of bronchoalveolar lavage fluid (BALF) were performed. RESULTS: Compared to the room-air control, hyperoxia group developed severe lung damage. There were a significant increase in lung wet/dry weight ratio (5.57±0.29 vs 5.29±0.25, t=2.29, P<0.05) and the protein content (1.49 g/L vs 0.32 g/L, t=28, P<0.05) and cell count (139.70×10 7 /L vs 16.30×10 7 /L, t=21, P<0.05) in BAL. eNOS mRNA expression in the hyperoxia group were significantly elevated (1.02±0.06 vs 0.70±0.12, t=6.36, P<0.01). The mean iNOS mRNA expression also showed an increase in the hyperoxia group, although the difference was not statistically significant. This was associated with significantly higher pulmonary eNOS, iNOS protein expression (8.8±0.8 vs 4.5±1.0, t=8.14, P<0.01 and 4.6±0.6 vs 3.2±0.6, t=3.21, P<0.05) in the hyperoxia group. CONCLUSION: Hyperoxic exposure of preterm rat pups causes upregulation of NOS gene expression, which persists even in established oxygen-induced lung damage. Endogenous NOS may play an important role in the pathphysiology of pulmonary oxygen injury in premature animal.