The purpose of this study was to determine whether the amount of alveolar epithelial tissue damaged during exposure of NO2 could be quantified by measuring the proliferative response to Type 2 cells. To accomplishe this, we used tissues from previously published experiments in which rats had been exposed to NO2 and the proliferative response to Type 2 cells had been measured during a 5-day period. The proportion of alveolar epithelium damaged was determined by stereologic examination with electron microscopy of tissue sections from those rats exposed to NO2 for 24 hours. These values were then compared with the total proliferative response to Type 2 cells for the 5 days of exposure. The study demonstrated that increasing tissue damage is assocaited with a greater proliferative response to Type 2 cells. The high degree of correlation (r = 0.93) indicates that the proliferative response of Type 2 cells can be used as an indirect means to quantify acute damage to the alveolar epithelium.

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