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Activation and increment of alveolar macrophages induced by nitrogen dioxide
Abstract:
Male Wistar rats were exposed to 4 ppm nitrogen dioxide (NO2) 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 less than 0.001) and 1.17-fold (p less than 0.05) those of the control values, respectively. The specific activities of succinate-cytochrome c reductase of the mitochondrial respiratory system and pyruvate kinase of the glycolytic pathway also increased to 1.17-fold (p less than 0.01) and 1.20-fold (p less than 0.01) those of the control values, respectively. In addition, the incorporation of [3H]leucine and [14C]thymidine into alveolar macrophages were elevated to 1.77-fold (p less than 0.001) and 1.84-fold (p less than 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 less than 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 micron in diameter), and most of them were distributed between 11 and 17 micron in diameter. Exposures to 4 ppm NO2 increased significantly the cells of 9-13 micron in diameter on the seventh day. These results show that exposures to 4 ppm NO2 cause a metabolic enhancement and subsequent increase in alveolar macrophages.
Insights
Exposure to nitrogen dioxide (NO2) enhances alveolar macrophage metabolism and increases their numbers in rats. These effects return to normal levels by day 10.
Area of Science:
- Environmental toxicology
- Cellular immunology
- Pulmonary toxicology
Background:
- Nitrogen dioxide (NO2) is an environmental pollutant with known respiratory effects.
- Alveolar macrophages are key immune cells in the lungs, crucial for defense and homeostasis.
Purpose of the Study:
- To investigate the effects of sub-chronic NO2 exposure on alveolar macrophage metabolism and numbers.
- To determine the temporal response of alveolar macrophages to NO2 inhalation.
Main Methods:
- Male Wistar rats were exposed to 4 ppm NO2 for 10 days.
- Alveolar macrophages were collected via pulmonary lavage at various intervals.
- Enzyme activities (metabolic and mitochondrial) and cellular incorporation of radiolabeled precursors were measured.
- Macrophage size distribution was analyzed.
Main Results:
- NO2 exposure led to a significant metabolic enhancement of alveolar macrophages, indicated by increased activities of key enzymes in peroxidative and glycolytic pathways.
- Uptake of [3H]leucine and [14C]thymidine into macrophages increased, suggesting elevated protein and DNA synthesis.
- The number of alveolar macrophages increased significantly by day 7 and remained elevated through day 10.
- NO2 exposure altered the size distribution of alveolar macrophages, increasing the proportion of smaller cells (9-13 micron).
- Enzyme activities returned to control levels by day 10.
Conclusions:
- Sub-chronic exposure to 4 ppm NO2 induces a transient metabolic enhancement and proliferation of alveolar macrophages in rats.
- These cellular changes suggest an inflammatory or adaptive response to NO2-induced lung injury.
- The observed effects are reversible, with normalization by day 10 of exposure cessation.