Morphometric study on age-dependent pulmonary lesions in rats exposed to nitrogen dioxide.

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Electronmicroscopic morphometry was performed on lung of 1, 3, 12 and21 months-old rats exposed to 0.1, 0.5, 3 and 10 ppm nitrogen dioxide (NO2) continuously for one month. The rats used in this experiment were all supplied at one time from one colony and kept uder a barrier system until exposure. Effects of aging on the responses of lungs to NO2 were studied by comparingthe dose-effect reaction patterns among the age groups. A trend of dose-dependent increase of arithmetic mean thickness of air-blood barrier was found in all age groups examined. The responses of lung to NO2 ex-posure showedage-related differences. Based on the morphometric index, the response declines from 1 to 12 months, but increases again in 21-months-old rats. The compartmental components of alveolar wall tissue such as type I epithelial cells, type II epithelial cells, interstitial cells, interstitial matrix and capillary en-dothelium appeared to have various degrees of response due to both age at onset of exposure and NO2 concentration, resulting in the appearance of varying stages in impairment or repair. Accordingly, the response of each compartmental com-ponent of lung to the concentrations of NO2 did not always exhibit a simple dose-dependent increase or decrease but sometimes indicated a multiphasic reaction pattern.
独立行政法人労働安全衛生総合研究所の論文