Ozone-induced acute pulmonary fibrosis in rats. Prevention of increased rates of collagen synthesis by methylprednisolone.

The net rate of collagen synthesis by lung minces prepared from rats exposed for 7 days to 0.8 to 1.5 ppm (1.6 to 3.0 mg/m3) of ozone was increased in a dose-dependent manner severalfold above the net rate obtained with lung minces prepared from rats that had breathed only filtered air. Concurrent administration of methylprednisolone (1 to 50 mg/kg/day) during the exposure to ozone prevented the increase in rate of collagen synthesis in a dose-dependent manner for each level of ozone tested. These results could be correlated with lower levels of inflammatory edema measured in the same steroid-treated rats as decreased wet weights of their right apical lung lobes. We conclude that acute pulmonary fibrosis caused by exposure of rats to high levels of inspired ozone can be partially or completely prevented, depending on the severity of the insult, by simultaneous administration of high levels of the anti-inflammatory steroid methylprednisolone.