The Study On Dynamic Changes Of Apoptosis And Proliferation Of Lung Cells, Interstitial Fibrosis And Their Mechanisms In Premature Rats With Hyperoxia-induced CLD

Hypoxia is the most common clinical manifestation in premature infants suffering from cardiac and pulmonary disease, and also one of the important reasons leading to irreversible lesion of central nervous system. So, enough precautions and attentions should be paid on the hypoxia of premature infants. However oxygen is a gas drug, and infants who exposed to higher levels of supplemental oxygen were found to have different kinds of lesions in pulmonary tissue, even to have chronic lung disease ( CLD). Although mechanical ventilation of high PIP and infection can both lead to CLD, higher levels of supplemental oxygen is thought to be the most important reason and high-risk factor resulting in CLD so far. Recently, with the rise of survival rate hi extremely low birth weight infants , the morbidity of CLD has got 30% ~ 40% abroad, and has a rising tendency in our country year by year. Its pathogenic mechanisms are not fully understood, so there are not effective control methods or preventive measures. Topics on CLD become the most challenging in neonatal field.At present accepted pathogenic mechanisms of CLD are mainly described as following; 1) Because of the deficient antioxidant system of premature baby oxygen free radicals and reactive oxygen species were overproduced after inspiring higher concentration of supplemental oxygen, and unbalanced oxidant/antioxi-dant system eventually leads to pulmonary lesions; 2) In early stage, inflammatory cells ( especially pulmonary alveolar macrophages) converge into the lungproducing continually many proinflammatory factors such as IL-6, IL-8, and TNF-a that make lots of neutrophils migrate from the vascular into the lung, which causing inflammation by releasing oxygen free radicals and proteases and so on.It was thought that pulmonary interstitial fibrosis is the main pathological change in CLD, but now more and more scholars in the world noticed that lung development retardation is another important factor affecting prognosis of CLD; there are different conclusions on apoptosis in pathology and proliferation of lung cells in hyperoxia-induced CLD. And there are few investigations about the role of type II alveolar epithelial cell ( AEC- II ) in pulmonary epithelia remodeling and the interstitial fibrosis.The aims of the study were at investigating dynamic pulmonary morphology change and at studying weather there are increased apoptosis and increased or decreased proliferation of lung cells as well as interstitial fibrosis and their pathogenic mechanisms in hyperoxia-induced premature rats. We try to provide more information of pathophysiological mechanism of CLD.Material and Methods1. Animal modelPremature pups were delivered by cesarean section at 21 days of gestational age and pool together in 2-3 litters and then randomly redistributed to surrogate mother rats. In the same experiment, the pups of model group were placed in 90% oxygen, and pups of control group remained in room air. Nursing mothers were rotated between oxygen-exposed and room air litters every 24 hrs to avoid oxygen toxicity and to eliminate maternal effects between groups. Oxygen exposures were done in 3-ft plexiglas chamber into which oxygen was continuously delivered at 2. 0L/min. Continuous flow achieved a constant level of 90% oxygen and the carbon dioxide concentration was <0. 5%. Temperature and relative humidity were maintained at 22C -25C and 50% ~70% respectively. For a daily 30min period, the chamber was opened to allow provision of fresh food and water, weighing of the rat litter, and exchange the surrogate mothers be-tween the two groups.2. Sample collection and treatmentAnimals were killed by an intraperitoneal injection of pentobarbital sodium and exsanguinated by aortic transaction on day 1, 3, 7, .14 and 21. The thorax was opened and lung tissue was collected and stored respectively according to the following methods: some samples was fixed in 4% fonnaldehydum polymeri-satum and some in 2.5% glutaral and residual sample in the RNase-free Eppe...