Circulating factors that modify lung cell DNA synthesis following exposure to inhaled oxidants. II. Effect of serum and lavage on lung pneumocytes following exposure of adult rats to 1 ppm ozone

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Abstract
Adult rats were exposed to 1 ppm (1.96 mg/m3) ozone or air for 2 wk. Animals were sacrificed at 3, 5, 7, or 14 d after the onset of exposure, and samples of plasma and lung lavage were obtained. Heat‐inactivated plasma and lavage from animals exposed to ozone for 5 or 7 d significantly increased DNA synthesis by lung pneumocytes compared with plasma or lavage from air‐exposed animals. Fractionation of plasma and lavage samples indicated that the factor responsible had an isoelectric point of 6.45–6.75, and a molecular weight of 38 ± 3 kDa. This factor has a dose‐dependent effect on lung pneumocyte DNA synthesis in culture. It has no effect on cultured fibroblast DNA synthesis, and is distinct from a previously described factor in the plasma of these ozone‐exposed animals that enhances fibroblast DNA synthesis. The factor is detectable within 5 d of exposure, and may hold some promise as a marker of early oxidant lung injury.