Sulfuric Acid Aerosol Induces Changes in Alveolar Surface Tension in the Guinea Pig but Not in the Rat

Abstract

The purpose of this study was to investigate the effects of an acid aerosol, at high concentration, on the surface properties of the extracellular fluid lining the airways and alveolae. Guinea pigs and rats were exposed to 43 mg/m3 and 94 mg/m3 of sulfuric acid aerosol mass median aerodynamic diameter (MMAD) 0.9 micron or water aerosol (control), respectively, for 4 hours in an exposure chamber. Surfactant material was extracted from bronchoalveolar lavage fluid (BAL) by centrifugation, and phospholipid, protein, and cell concentrations measured. The extract was reconstituted to 300 micrograms/mL of phospholipid, and its surface properties assessed with a captive bubble surfactometer. The minimum surface tension for the acid-exposed guinea pig BAL was 12.1 +/- 8.48 (mean +/- SD) mN/m, which was significantly higher than the control group, 2.0 +/- 0.43 (mean +/- SD) or the acid-exposed rats, 1.29 +/- 0.11 (mean +/- SD). The change in film area obtained by compressing the film from equilibrium surface tension (25 mN/m) to its minimum value (gamma 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 inhibition was found to be the maximum film compressibility (Cmax) 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 the BAL. There was no change in total phospholipids. By contrast BAL retrieved from rats exposed to approximately twice the concentration of acid aerosol showed no cellular nor biochemical abnormalities and its surface tension properties were normal. We conclude that the abnormalities of surfactant activity in the acid-exposed guinea pigs result from the cellular and humoral responses of acute lung injury rather than a direct effect of acid.