Effects of chronic exposure to ozone on collagen in rat lung.

Pulmonary fibrosis is a consequence of severe injury from some toxic agents including high doses of ozone. It is not known, however, whether chronic exposure to low doses of ozone, such as those encountered in polluted ambient atmospheres, could also result in abnormal accumulations of lung collagen. Rats were exposed to ozone for 20 hr per day, 7 days per week for 3, 6, 12, and 18 months at concentrations of 0.12, 0.25, or 0.50 ppm. Controls were exposed under identical conditions to purified air. Upon removal from the chambers, rats were euthanized and lung tissue slices incubated with [14C]proline. The incorporation of 14C into hydroxyproline and the total hydroxyproline content of lung tissue were measured as estimates of lung collagen synthesis and content, respectively. The formation of labeled hydroxyproline tended to decrease significantly with time in controls and at the three ozone doses. There were, however, no significant dose-related changes at any of the time points tested. Total lung hydroxyproline increased with age in all groups, but no dose-related changes were detected at any time point. It was concluded that chronic exposure of rats to ozone at concentrations which approximate ambient urban concentrations did not affect normal age-related changes in either synthesis or accumulation of lung collagen.