UC Irvine

Sprague-Dawley rats (n=10 per group) were exposed while exercising for 3.0 h to 1) clean air, 2) 0.35 ppm O3, 3) 0.6 ppm NO2, or 4) 0.35 ppm O3 + 0.6 ppm NO2. Relative humidity was 40%. Exercise (running at 15 m/min and 20% grade) elevated metabolic gas exchange by a factor of 2.5 over resting metabolism. 48 h post exposure, lungs were removed, fixed, sectioned, and stained. Sections were scored for % area of parenchyma involved in focal lesions induced by the pollutants. Exposure to NO2 alone resulted in no detectable difference in lung tissues compared to clean air control animals. Exposure to O3 induced focal parenchymal lesions. However, O3 is combination with NO2 resulted in increases in lesion areas by a factor of 2 over those for O3 alone. The mixture of oxidants formed HNO3 vapor at a concentration of 0.05 mg/m3 during the exposure. The synergistic response observed between O3 and NO2 in the mixture may be due to the presence of nitric acid vapor, or to other possible reaction products such as N2O5 and nitrate radical.