Nitrogen Dioxide and Pulmonary-Proteolytic Enzymes

Abstract

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 cathepsins 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.