Cell proliferation in lung following acute fly ash exposure

Cell proliferation was examined in the lung parenchyma, the ciliated airway epithelium and the lymph nodes of Fischer-344 rats following a 6-h exposure to fly ash obtained from the baghouse of an experimental fluidized bed combustor. The fly ash concentration was 142 mg/m3 with a mass median aerodynamic diameter (MMAD) of approximately 3.0 micron and a geometric standard deviation (sigma g) of approximately 2.6. Lung deposition of fly ash was measured in the right lung to be 90 +/- 20 and 80 +/- 30 mg for male and female rats, respectively, resulting in a calculated value for male rats of (140 +/- 30 micrograms/animal) and for female rats of 130 +/- 50 micrograms/animal). Autoradiographic methods were used to detect cells that incorporated [3H] thymidine. About a 10-fold increase in labeling of the lung epithelial type II cells was observed following the 6-h fly ash exposure. There was also an increase in [3H] thymidine incorporation into DNA of alveolar macrophages. Labeling activity of macrophages within the lung was increased for up to 4 days following fly ash exposure; however, the size of the macrophage population was not altered. Following exposure, a higher labeling index was also observed in the epithelial cells of the airways. Labeling in the trachea reached a peak at 4 days after exposure while in the bronchi and in small airways (inside diameter of less than 0.35 mm) the highest level of labeling was observed at 1 day after exposure. Labeling in airway epithelial cells was increased 2-4 times above that of sham-exposed animals. Lung-associated lymph nodes accumulated particulate material and had variable amounts of [3H]thymidine incorporation. These results demonstrate that acute inhalation exposure to fly ash initiated cell division or DNA synthesis in several cell populations of lung parenchyma and airways.