Abstract 1931

Meconium Aspiration Syndrome (MAS) is a major cause of newborn mortality and morbidity. About 1500 newborn die a year from this disease in the United States. In this report we investigated biological response and morphological changes of the newborn lungs after meconium instillation. We developed a model for the studies of MAS using 2 weeks old rabbit pups. Total of 46 pups were studied. 10% human meconium was injected via endotracheal tube and rabbit pups were sacrificed at 2, 4, 8 and 24 hrs. Another control rabbit pups received same volume of 0.9% NaCl, instead of meconium, and were sacrificed at 5 different time points similar to the study group. Then trachea was cannulated and lung lavage was obtained. Tracheal lavage fluid was spun and cells were isolated and identified into macrophages, neutrophils and necrotic. Necrotic cells were characterized by disrupted or lysed cells or nuclei membranes. Apoptotic cells were characterized by staining with Ethidium Bromide or 4′-6′-diamino-2′-phenylidone (DAPI) and identified by cells shrinkage, swelling and changing of their morphology. DNA fragmentation during apoptosis or necrosis was studied by in situ end labeling (ISEL) method. The data show significant increase of necrotic cells and neutrophils in meconium treated lungs. The necrotic cells in control group increased 2 fold from the pretreatment to the 24 hours. But in meconium group the increase was over 4.5 fold. The neutrophils count in controls did not change from pre saline instillation to 24 hrs. In meconium group neutrophils steadily increased after instillation reached the peak at 24 hrs over 7 fold. There were no differences in % of macrophages between control and meconium group either pretreatment or post treatment. These observations were also supported by histological studies using Hematoxylin/Eosin staining. Meconium aspiration resulted selectively in loss of airway and alveolar cells followed by cell death. We have shown detachment of the airway epithelium cells and characteristic DNA fragmentation in meconium affected lungs which increased in time dependent fashion. These findings demonstrate the deleterious effect of meconium include both apoptosis and necrosis of airway and alveolar epithelial cells. (Table)

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Funded by Research and Education Foundation at M.Reese Medical Stuff, Chicago, Illinois