DIFFUSE ALVEOLAR DAMAGE IN THE RAT LUNG AFTER SHORT AND LONG-TERM EXPOSURE TO NITROGEN-DIOXIDE

In order to quantify parenchymal, vascular and epithelial changes occurring in the exudative and organizing phase of diffuse alveolar damage (DAD) induced by inhaled NO2 groups of 7 rats were continuously exposed to 5, 10 or 20 ppm NO2 for 3 and 25 days alternatively. AgNOR analysis revealed the highest proliferative activity in the epithelium of the respiratory bronchioles. In this region already after 3d exposure to 5 ppm the maximum AgNOR number was reached. In contrast to long-term exposure after 3d exposure to 5 and 10 ppm NO2 the AgNOR number in the respiratory bronchioles was significantly higher than in central airway epithelia. After long-term exposure to 5 and 10 ppm AgNOR number decreased to normal values or showed no further significant increase, long-term exposure to 20 ppm resulted in a further increase of the AgNOR number. A significant increase of the alveolar circumference and decrease of alveolar surface density was found after an exposure to 20 ppm for 3d and long-term exposure to 10 and 20 ppm NO2, whereas the S ppm exposure groups disclosed no significant change of these values. Medial hypertrophy was detected after exposure to 10 and 20 ppm NO2 for 25 days, after the exposure to 5 ppm for 3d and 25d medial thickness was significantly decreased due to vasodilatation induced by NO, one of the major reaction products of NO2.