Chronic Toxicity of Nitrogen Dioxide

Abstract

Mice were exposed to 0.5 ppm nitrogen dioxide (NO₂) for 6, 18, and 24 hours daily. The lung alveoli were expanded in all mice exposed to NO₂ from three to 12 months, with the highest degree of involvement at 12 months; thus the number of expanded alveoli appeared to increase with exposure time. The general impression was of early bronchiolar inflammation with reduction of distal airway size and a concomitant expansion of alveoli. The overall lesions appeared to be consistent with the development of early focal emphysema. Examination of the heart, liver, kidney, and spleen did not reveal any unique pathology. Mice exposed to NO₂ and challenged with Klebsiella pneumoniae exhibited a marked reduction in functional lung tissue.