Changes in pulmonary phospholipid biosynthetic enzymes after nitrogen dioxide exposure

Abstract

The activities of phospholipid synthesizing enzymes and marker enzymes were measured in homogenates and subcellular fractions of lungs and livers of rats 2 days after exposure to 42 ppm nitrogen dioxide (NO 2) for 5 hr. DNA content of NO 2-exposed lungs increased 33% over air-exposed controls, while protein in all fractions was elevated about twofold. The ratios of wet to dry weight remained unchanged. The specific activity of microsomal glycerol-3-phosphate acyltransferase was 42% higher than controls, while phosphatidate phosphohydrolase and choline phosphotransferase were 26 and 20% higher in microsomal specific activity. The microsomal marker enzyme NADPH cytochrome c reductase showed similar specific activities in microsomes from NO 2 or air-exposed animals. Glycerolphosphate phosphatidyltransferase and the mitochondrial marker succinate cytochrome c reductase were higher in specific activity by 28 and 23% in mitochondrial fractions from NO 2-exposed lungs. Total lung activities of all enzymes measured were 80–180% higher in NO 2-exposed lungs. No changes in any of the measured parameters were observed in liver due to NO 2 exposure. These results are consistent with the generally observed proliferative response of lung cells after toxic insult. The large increase in total lung activity of phospholipid biosynthesizing enzymes suggests that the proliferating cells are enriched in these enzymes relative to other cell types.