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 occu rring in the exudative and organizing phase of diffuse alveolar damage (DAD) induced by inhaled NO2 groups of 7 rats were continuously expos ed to 5, 10 or 20 ppm NO2 for 3 and 25 days alternatively. AgNOR analy sis revealed the highest proliferative activity in the epithelium of t he respiratory bronchioles. In this region already after 3d exposure t o 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 th e respiratory bronchioles was significantly higher than in central air way epithelia. After long-term exposure to 5 and 10 ppm AgNOR number d ecreased to normal values or showed no further significant increase, l ong-term exposure to 20 ppm resulted in a further increase of the AgNO R number. A significant increase of the alveolar circumference and dec rease of alveolar surface density was found after an exposure to 20 pp m for 3d and long-term exposure to 10 and 20 ppm NO2, whereas the S pp m exposure groups disclosed no significant change of these values. Med ial hypertrophy was detected after exposure to 10 and 20 ppm NO2 for 2 5 days, after the exposure to 5 ppm for 3d and 25d medial thickness wa s significantly decreased due to vasodilatation induced by NO, one of the major reaction products of NO2.