An apparatus was designed and built for the constant pressure fixation of up to 48 small to medium sized animal lungs by tracheal perfusion. The system hae a 40-liter fixative capacity, automatically maintained selectable fixative fluid levels in all reservoirs, and filtered and recirculated fixation fluid for periods up to several days.

A 10-runway treadmill was enclosed for inhalation toxicological studies of rodents under exercise exposure to environmental pollutants. The exposure system was lined with sheet stainless steel to minimize scrubbing of charged particles and reactive gases. Average metabolic gas exchange of exercising animals was derived from measurements of inlet or outlet airflow and data from an O2 analyzer in conjunction with either a CO2 or N2 analyzer. An airflow rate of 400 l X min-1 ensured a response time of 1 min to reach 95% of a step change in metabolic rate and held scrubbing losses of an O3 test atmosphere to less than 2% of treadmill inlet concentration. Gas exchange averaged for 10 rats during incremental exercise up to their highest collective performance was similar to published data for rats tested individually.

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.