Nitrogen dioxide and pulmonary proteolytic enzymes. Effect on lung tissue and macrophages

Hamsters were exposed to 30 ppm nitrogen dioxide (NO2) for 2 and 50 days and sacrificed. Pulmonary lavage was carried out on a portion of each group to obtain an alveolar macrophage fraction. Proteolytic activity (P.A.), as measured by caseinolysis at pH 3.0 and pH 5.0, increased nearly twofold in the 2-day NO2 lung extracts and fourfold in the 50-day NO2 samples. P.A. in macrophage extract at pH 3.0 increased tenfold with both 2- and 50-day NO2 exposure. Lung extract hydrolysis of specific esterase and amidase substrates and susceptibility to activators and inhibitors of proteolytic enzymes are consistent with the presence of lysosomal cathepsin A, B1, B2, C, D, and E. The lack of NO2-induced increases in P.A. at physiologic values of pH may be the basis of the lack of significant pulmonary tissue destruction observed in rodents exposed to NO2 for 2 and 50 days.