PULMONARY RESPONSES OF RATS TO AMBIENT LEVELS OF OZONE - EFFECTS OF 7-DAY INTERMITTENT OR CONTINUOUS EXPOSURE

Abstract

Groups of Sprague-Dawley rats were exposed to ozone for either 8 or 24 h a day for 7 consecutive days to evaluate morphologic changes of the respiratory system. Three levels of exposure (0.2, 0.5 and 0.8 ppm of O3) were selected to simulate moderate to severe episodes of oxidant pollution in urban environments. Morphologic evaluation included light microscopy, scanning EM and transmission EM. Biochemical parameters which were examined included succinate oxidase, G-6-P dehydrogenase and NADP-cytochrome c reductase activities. Exposure to concentrations as low as 0.2 ppm for 7 days induced pulmonary damage; there was a dose-dependent pulmonary response to the 3 levels of ozone which was quantitated by alterations in biochemical marker enzyme activities and observed morphologically; proportionate differences were not observed in morphologic characteristics of the lesions or detected in biochemical parameters between rats exposed continuously for 7 days and those exposed intermittently for 8 h a day for 7 consecutive days; alterations in surface height and granularity of the cytoplasmic luminal projection of Clara cells were subtle changes which were dose-dependent, occurring even at the lowest ozone concentration, and best detected by scanning EM; alveolar macrophage accumulation within proximal alveoli of alveolar ducts was the most readily detectable morphologic indicator of pulmonary damage; and although the brunt of ozone damage was borne by the centriacinar region, there was damage to cilia and increased ciliogenesis occurring in the trachea and larger conducting airways following exposure of 0.5 and 0.8 ppm of ozone.