Consequences of prolonged inhalation of ozone on F344/N rats: collaborative studies. Part V: Effects on pulmonary function.

The impact of a 20-month exposure to ozone on the pulmonary function of rats was assessed from a single series of measurements made after exposures were completed. Four to ten male and female F344/N rats per group were exposed six hours per day, five days per week, for 20 months to ozone at 0.12, 0.5, or 1.0 parts per million (ppm), or to clean air as controls. One to three days after the last exposure, the rats were anesthetized using halothane, fitted with oral endotracheal and esophageal catheters, and measured using plethysmographic techniques. The differences between mean values for control and treated rats were tested for significance by multiple comparisons. The values and intersubject variability for more than 30 measured and calculated parameters were similar to those reported previously for rats of similar age. The only consistent exposure-related effect was a small reduction of residual volume measured during slow lung deflation. This trend was observed in most exposure groups, but was most significant in females exposed to ozone at the 0.5 ppm level. Fibrosis and epithelial changes were observed in the terminal bronchiole-alveolar duct region in parallel studies of different rats from the same exposure groups. We hypothesized that these changes stiffened airspace walls and acted to maintain the patency of the air pathway at a lower than normal lung volume during deflation. Overall, the exposures had little impact on the integrated pulmonary function of the lung as measured in anesthetized rats.