Morphometric evaluation of pulmonary lesions in rats exposed to ozone

Four hours exposure to 3 ppm ozone produces morphometrically quantifiable alterations in the lungs of rats. Lungs of exposed rats were fixed either immediately after exposure or after a 12-hour recovery period, and the tissue was evaluated using stereologic technics with both the light and electron microscopes. Immediately after exposure, the volume fraction of nonparenchymal tissue was larger (0.057) than for controls (0.045); that of the lumina of large vessels decreased (0.039) from the control value (0.059). The nonparenchymal tissue fraction was 0.053 12 hours later, while the luminal fraction (0.054) resembled the control value. The volume fractions of parenchyma, total tissue and air space showed only slight changes. Ozone also affects all three components of the air-blood barrier, primarily by the production of intracellular edema. The arithmetic mean thickness of the pulmonary blood-air barrier increased from 1.385 +/- 0.095 mu in unexposed rats to 1.700 +/- 0.189 mu in rats immediately after exposure. The primary increase was in thickness of membranous epithelial and capillary endothelial cells. Partial recovery of total barrier thickness (1.582 +/- 0.292 mu) occurred 12 hours after exposure.