Phase-dependent response of the lung to NO2 irritant insult.

The biochemical and histopathological response of the lung following acute and repeated (subacute) exposure to nitrogen oxide (NO2) was examined. Activities of lactate dehydrogenase, beta-glucuronidase, choline kinase, and protease inhibitor were measured in murine pulmonary tissue immediately and two days following exposure. Nonenzymatic parameters, pulmonary protein content, and wet lung weight were also monitored. Immediately following acute exposure to NO2, only the nonenzymatic parameters were elevated. By two days following acute exposure, following subacute exposure; however, the nonenzymatic parameters were attenuated with respect to the enzymatic activities. The lung exhibits a dynamic response following damage by oxidants such as NO2. This response is divided into three distinct phases (exudative, proliferative, and tolerant), which can be characterized both biochemically and histopathologically.