ARE CHANGES IN BREATHING PATTERN ON EXPOSURE TO OZONE RELATED TO CHANGES IN PULMONARY SURFACTANT

Rats respond to the inhalation of ozone with changes in breathing patt ern during the exposure and the development of a pulmonary inflammator y response 24-48 h postexposure. We report experiments designed to inv estigate the relationships between changes in breathing pattern and th e composition and surface tension-reducing properties of pulmonary sur factant immediately after the exposure. A total of 64 male Fischer 344 rats were exposed to 0.8 ppm O3 for 4 h in 4 replicate exposures with matched purified air control exposures and 8 rats per exposure group. Those exposed to O3 developed the rapid-shallow breathing pattern cha racteristic of oxidant pulmonary irritation during exposure. The rats were sacrificed immediately following the exposure, and pulmonary surf actant was isolated from samples of bronchoalveolar lavage fluid poole d from groups of eight rats. After esterification, the fatty acid meth yl ester composition was measured using GC-MS. In the ozone-exposed an imals, the decreases in unsaturated species (linoleic, oleic, palmitol eic, and an unidentified fatty acid) relative to the major saturated c omponent, palmitic acid, were highly statistically significant, while stearic acid showed no significant change. Total protein in the lavage fluids of the exposed animals was not elevated, indicating that sacri fice and analysis were performed early in the O3 injury-inflammation r esponse sequence, and suggesting that the fatty acid changes in the pu lmonary surfactant may be due in part to a direct reaction with inhale d O3. The group mean change in breath frequency (as percent of matched purified air control values) was significantly correlated with the pe rcent change in linoleic acid fraction among replicate exposures, sugg estive of a possible relationship between ozone-induced changes in pul monary surfactant and changes in breathing patterns. There was no sign ificant change in the surface pressure-area isotherms of monolayers of pulmonary surfactant upon ozone exposure. However, comparison to isot herms from an in vitro exposure of a synthetic mixture of saturated an d unsaturated phospholipids suggests that changes due to the observed change in the fatty acid composition in the in vivo experiments may be too small to be observed. Furthermore, the pulmonary surfactant isola tion procedure was specifically designed to recover the undamaged surf actant and may discriminate against products of reaction with ozone; h ence the isotherms may not necessarily reflect the actual changes duri ng the exposure. Further experiments to elucidate the interaction of i nhaled O3 with pulmonary surfactant and its relationship to changes in breathing pattern are discussed.