Ozone-induced alterations in collagen metabolism of rat lungs: II. Long-term exposures

Abstract

Rats were exposed to 0.5 ppm of ozone delivered for 23.5 hr per day for up to 180 days. One group of rats was allowed to breathe filtered air for about 2 months after the conclusion of the exposure. Lung collagen and total-protein synthesis rates were quantitated by biochemical analyses performed with lung minces. Other lung lobes from the same rats were used to quantitate collagen and total protein content. Increased levels of lung protein and of lung collagen (hydroxyproline) content were observed at all times sampled during exposure to ozone (3, 30, 50, 88, 180 days); the observed lung hydroxyproline content at 180 days persisted during the 2 months of postexposure recovery. Collagen synthesis rates measured in lung minces were elevated in the exposed rats at all times sampled, consistent with the observed increased lung collagen content seen throughout the study. The observed biochemical changes were consistent with concurrent morphological observations of the occurrence of mild pulmonary fibrosis.