INFLUENCE OF ACID AEROSOL DROPLET SIZE ON STRUCTURAL-CHANGES IN THE RAT LUNG CAUSED BY ACUTE EXPOSURE TO SULFURIC-ACID AND OZONE

To investigate whether aerosol droplet size influences structural chan ges in the lung produced by short-term, concomitant exposure to ozone and sulfuric acid, groups of 10 rats were exposed 4 hr/day for 2 days to filtered air, 0.6 ppm ozone, 0.5 mg/m(3) fine (aerosol mass median diameter (MMD) = 0.3 mu m) or ultrafine (MMD = 0.06 mu m) sulfuric aci d, or a mixture of ozone and 0.5 mg/m(3) fine or ultrafine sulfuric ac id. The volume percentage of total parenchyma containing markedly to s everely injured alveolar septae was measured morphometrically. There w ere no differences between the ultrafine or fine acid exposure groups and the sham group for any of the morphologic endpoints. Volume percen tage of markedly to severely injured tissue was increased in the ultra fine, but not fine, mixture animals when compared with the ozone-only group. In addition, a synergistic interaction between ozone and ultraf ine, but not fine, sulfuric acid was found for this endpoint. The brom odeoxyuridine cell labeling index in the periacinar region was greater in the rats exposed to the fine sulfuric acid and ozone mixture than that in rats exposed to ozone alone, and a synergistic interaction bet ween ozone and fine sulfuric acid was found for this end point. None o f the exposures produced any changes in ventilatory parameters. Thus, acid aerosol droplet size was found to influence the effect of sulfuri c acid in modifying ozone-induced structural changes in the rat lung. (C) 1997 Academic Press.