PULMONARY-FUNCTION ALTERATIONS IN F344 RATS FOLLOWING CHRONIC OZONE INHALATION

The impact of a 20-mo exposure to ozone on the pulmonary function of r ats was assessed by performing a single series of measurements after e xposures were completed. Four to 10 male and female F344 rats per grou p were exposed 6 h/day, 5 days/wk for 20 mo to ozone at 0.12, 0.5, or 1.0 ppm, or to clean air as controls. One to 3 days after the last exp osure, the rats were anesthetized using halothane, fitted with oral en dotracheal and esophageal catheters, and measured using plethysmograph ic techniques. The significances of differences between mean values fo r control and treated rats were tested by multiple comparisons. The va lues and intersubject variability for over 30 measured and calculated parameters were similar to those reported previously for similarly age d rats. The only consistent exposure-related effect was a small reduct ion of residual volume measured during slow lung deflation. This trend was observed in most exposed groups, but was most significant in fema les at the 0.5 ppm level. Fibrosis and epithelial changes were observe d in the terminal bronchiole-alveolar duct region in parallel studies of different rats from the same exposure groups. It was hypothesized t hat these changes stiffened airspace walls and acted to maintain the p atency oi the air pathway to a lower than normal lung volume during de flation. Overall, the exposures had little impact on the integrated pu lmonary function of the lung as measured in anesthetized rats.