Sulfuric acid aerosol induces changes in alveolar surface tension in the guinea pig but not in the rat

The purpose of this study was to investigate the effects of an acid aerosol , at high concentration, on the surface properties of the extracellular flu id lining the airways and alveolae. Guinea pigs and rats were exposed to 43 mg/m(3) and 94 mg/m(3) of sulfuric acid aerosol mass median aerodynamic di ameter (MMAD) 0.9 mu m or water aerosol (control), respectively,for 4 hours in an exposure chamber. Surfactant material was extracted from bronchoalve olar lavage fluid (BAL) by centrifugation, and phospholipid, protein, and c ell concentrations measured. The extract was reconstituted to 300 mu g/mL o f phospholipid, and its surface properties assessed with a captive bubble s urfactometer. The minimum surface tension for the acid-exposed guinea pig B AL was 12.1 +/- 8.48 (mean +/- SD) mN/m, which was significantly higher tha n the control group, 2.0 +/- 0.43 (mean +/- SD) mN/m, or the acid-exposed r ats, 1.29 +/- 0.11 (mean +/- SD). The change in film area obtained by compr essing the film from equilibrium surface tension (25 mN/m) to its minimum v alue (y(min)) was 62.9+/-13.83 (mean +/- SD)% for acid-exposed guinea pigs, compared to 16.3 +/- 5.77 (mean +/- SD)% for the control guinea pigs.;The most sensitive index of surfactant inhibiion was found to be the maximum fi lm compressibility (C-max) of the compression isotherm. This index was 119 times greater for the acid-exposed guinea pigs compared to control animals. These abnormalities were associated with an elevation of total protein (0. 95 +/- 0.33 [mean +/- SD] mg/ml compared to 0.13 +/- 0.03 [mean +/- SD] mg/ mL in controls) and polymorphonuclear leucocytes in Me BAL. There was no ch ange in total phospholipids. By contrast BAL retrieved from rats exposed to approximately twice the concentration of acid aerosol showed no cellular n or biochemical abnormalities and its surface tension properties were normal . We conclude that the abnormalities of surfactant activity in the acid-exp osed guinea pigs result from the cellular and humoral responses of acute lu ng injury rather than a direct effect of acid.