Activation and increment of alveolar macrophages induced by nitrogen dioxide

Abstract

Male Wistar rats were exposed to 4 ppm nitrogen dioxide (NO ₂ ) for 10 d, and at intervals alveolar macrophages were collected by pulmonary lavage. A metabolic enhancement of alveolar macrophages was observed on d 4 of exposure. The specific activities of glucose‐6‐phosphate dehydrogenase and glutathione peroxidase of the peroxidative metabolic pathway increased to 1.29‐fold ( p < 0.001) and 1.17‐fold (p < 0.05) those of the control values, respectively. The specific activities of succinate‐cy‐tochrome c reductase of the mitochondrial respiratory system and pyruvate kinase of the glycolytic pathway also increased to 1.17‐fold (p < 0.01) and 1.20‐fold (p < 0.01) those of the control values, respectively. In addition, the incorporation of [ ³ H]Ieucine and [ ¹⁴ C]thymidine into alveolar macrophages were elevated to 1.77‐fold (p < 0.001) and 1.84‐fold (p < 0.01) those of the control values, respectively. The activities of all enzymes tested decreased to control levels by d 10.

The number of alveolar macrophages collected from exposed animals increased to 1.24‐fold (p < 0.01) that of the control value on d 7 and was maintained at a significantly higher level until d 10. Alveolar macrophages were heterogeneous in size (7–21 μm in diameter), and most of them were distributed between 11 and 17 μm in diameter. Exposures to 4 ppm NO ₂ increased significantly the cells of 9–13 μm in diameter on the seventh day.

These results show that exposures to 4 ppm NO ₂ cause a metabolic enhancement and subsequent increase in alveolar macrophages.