Lysosomal enzyme activities in pulmonary macrophages from rabbits breathing iron oxide.

The effects of an in vivo exposure to a nontoxic particle, iron oxide, on lysosomal hydrolases in pulmonary macrophages were examined. Rabbits breathed a submicron-sized aerosol of iron oxide for 3 h (mass concentration, 186 to 222 mg/m3). Macrophages were recovered by lung lavage 0, 12, 18, and 24 h later. The number of cells lavaged after iron oxide was significantly greater than the control number, whereas the amount of protein recovered per 10(8) cells decreased, suggesting the influx of smaller cells. Macrophages from animals exposed to iron oxide reacted histochemically for acid phosphatase showed increased stain intensity and redistribution of enzyme within the cytoplasm. Considerable cell-to-cell variability in enzyme activity was evident in these macrophages. Homogenates of cells exposed to iron oxide assayed for 6 lysosomal acid hydrolases showed little change in specific activity or in total enzyme per 10(8) cells when compared to homogenates of cells from control animals. Sucrose density gradient centrifugation demonstrated that exposure to iron oxide caused an increase in lysosome heterogeneity over that seen in control preparations and the appearance of a population of lysosomes of increased density. An aerosol of iron oxide did not greatly alter the average concentrations of lysosomal enzymes in pulmonary macrophages, but did stimulate recruitment of new cells and thus increases the total amount of some enzymes in the lung.