A control group of 12 dogs and a treatment group of 6 dogs were exposed 16 hours daily for 68 months to filtered air and ambient concentrations of nitrogen dioxide (1.2 mg/m3), respectively. After subsequent exposure to clean air for three years, the dogs were necropsied and the right lungs fixed via intratracheal perfusion. Tissue samples were taken from each of the four right lungs, for light microscopy, scanning and transmission electron microscopy. The most common pattern of tissue destruction observed in lungs exposed to nitrogen dioxide was dilitation of alveolar ducts with short interalveolar septa; however, trabeculae were observed in regions of more severe tissue destruction. Loss of interalveolar septa accounted for a significant decrease in alveolar and capillary surface density. The ratio of capillary to alveolar surface density was not different between groups and thus indicates little change in the remaining interalveolar septa. Ultrastructural quantitation revealed a harmonic mean thickness identical to controls, whereas the arithmetic mean thickness was significantly increased in the nitrogen dioxide group. The increased thickness was primarily a result of collagen deposition between capillaries; however, the deposition did not impair the diffusible region of the alveolocapillary membrane. Numerical densities of alveoli were significantly decreased in the nitrogen dioxide group, whereas total alveoli of the right lung were not significantly decreased at the 0.05 level. Numerical densities and total number of alveolar ducts in the right lung were both significantly decreased as were the numerical profile density of respiratory bronchiles and alveoli within respiratory bronchioles. One possible explanation for the increase in alveolar number is compensatory alveolar hyperplasia of respiratory bronchioles and conversion to alveolar ducts in response to widespread interalveolar septal destruction in alveolar ducts of the nitrogen dioxide group. Scanning electron micrographs of terminal and respiratory bronchioles in similar regions of lungs of both groups demonstrated alveolar hyperplasia in first generation respiratory bronchioles and absence of third and fourth generation respiratory bronchioles in lungs exposed to nitrogen dioxide.
|Original language||English (US)|
|Number of pages||2|
|State||Published - 1980|
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