Effects of sulfur dioxide or ammonium sulfate exposure, alone or combined, for 4 or 8 months on normal and elastase-impaired rats.

Normal and lung-impaired rats were compared after exposure to SO2 and/or (NH4)2SO4 for 4 or 8 months, or for 8 months plus 3 months recovery. Young adult male Sprague-Dawley rats were pretreated intratracheally with either physiologic saline (normal lungs) or porcine pancreatic elastase (impaired lungs). Rats from each pretreatment group were exposed to filtered air (control), to SO2 (1 ppm) or (NH4)2SO4 (0.5 mg/m3), or to combined SO2 + (NH4)2SO4 for 5 hr/day, 5 days/week. Morphologic, physiologic, and immunologic criteria were evaluated. At 4 months cellular immunologic responsiveness was not impaired, but physiologic changes were detected. Morphologic changes were apparent in all time periods. Elastase-induced changes included greater lung volumes, emphysema, and alveolar interstitial fibrosis. Pollutant effects included bronchiolar epithelial hyperplasia and changes in alveolar mean chord length (MCL). Relative to controls, bronchiolar epithelial hyperplasia and MCL increased in saline/pollutant groups, but decreased in elastase/pollutant rats at 4 months. The pretreatment/pollutant interaction was not observed at 8 months. Elastase effects persisted throughout the recovery period. Pollutant effects were more transitory, although alveolar septal fibrosis was greater in saline/(NH4)2SO4 rats at 8 months. Pulmonary function changes associated with elastase included increases in residual volume, functional residual capacity, and the residual volume/total lung capacity ratios. The alveolar plateau of single-breath washout (N2 slope) was significantly steeper in elastase-treated rats but less steep in animals exposed to SO2 or to (NH4)2SO4 than in those exposed to air only.