TIME COURSE OF AIRWAY EPITHELIAL AND INFLAMMATORY CHANGES IN RATS EXPOSED TO MODERATE LEVELS OF OZONE

Abstract

This study determined the sequence of airway permeability and inflammatory changes in rats exposed to ozone O3 concentrations comparable to those encountered in the smog. Rats were exposed for a 3-h period to 0.15, 0.3, or 0.5 ppm O3. Since the results from other studies suggest that the times for the onset and peak of O3 effects are dependent on both the exposure concentration and the type of measured response, sets of rats were studied at 4-h intervals up to 24 h after exposure. An exposure to 0.5 ppm O3 did not produce a change in the protein and albumin levels in the bronchoalveolar lavage BAL immediately after exposure, but an increase in both of these measures occurred at 4 h after the end of exposure. Both protein and albumin levels peaked at the 8-h time point and then declined, but their overall concentrations remained higher than the control levels up to 24 h postexposure. In contrast to the protein and albumin levels in the BAL, polymorphonuclear leukocyte PMN number increased immediately postexposure, but the PMN peak at 8 h coincided with the protein and albumin peak at this time point. A slight decline in the PMN number was observed at the later time points, but a significant elevation in comparison to the controls matched a similar trend for protein and albumin. An exposure of rats to either 0.3 or 0.15 ppm O did not produce any change either in pro3 tein and albumin concentrations or in the PMN number in the BAL. This lack of O3 effect at concentrations near the ambient levels, which have been shown by others to produce airway changes in exercising humans, suggests that rats may be relatively less susceptible than humans. However, in human studies the exposures were performed while the subjects were exercising, and the alveolar dose for a given O3 concentration is believed to be much greater in humans than in rats.