Influence of Preexisting Pulmonary Emphysema on Susceptibility of Rats to Chronic Inhalation Exposure to Nitrogen Dioxide

Abstract

The effect of preexisting pulmonary emphysema on the susceptibility of rats to the effects of chronic inhalation exposure to nitrogen dioxide (NO₂) was examined. Rats were exposed 7 h/day, 5 daydweek for 24 months to 9.5 ppm NO₂ or sham-exposed to clean air. Emphysema was induced in one-half of the rats by intratracheal instillation of elastase 6 weeks before exposure began. Measurements included respiratory function, bronchoalveolar lavage, lung tissue collagen, clearance of radiolabeled tracer particles, excised lung weight and volume, histopathology, and mean linear intercept of terminal airspaces. Analysis of variance was used to detect significant interactions between the effects of emphysema and NO₂ Increased susceptibility was defined as a significant emphysema-NO₂ interaction that was greater than additive. Only one measured parameter met the criteria for increased susceptibility: a greater than additive effect was observed for the forced expiratory flow rate at 10% of forced vital capacity This finding was not supported by similar effects on closely related parameters, and could have occurred by chance among the 60 measured parameters at the p < .05 criterion used for statistical significance. The results of this study do not suggest that rats with elastase-induced pulmonary emphysema are more susceptible than normal rats to chronic exposure to high concentrations of NO₂