Change in properties of exogenous surfactant in injured rabbit lung.

We asked if the function of surfactant could be enhanced after exposure to injured lungs. We also asked if sensitivity to inhibition of the minimal surface-tension-lowering properties of surfactant by plasma could be altered. Lung injury in rabbits was induced with N-nitroso-N-methylurethane (NMU) and 6 of 17 NMU-injured rabbits were treated with 100 mg/kg surfactant. All rabbits were ventilated for 2 h, and large aggregate alveolar surfactant was isolated by centrifugation. In vivo function of the large aggregate surfactant was evaluated by treatment of preterm surfactant-deficient rabbits at 27 d gestation. Surfactant from NMU-injured lungs increased compliance from 0.37 +/- 0.01 in control preterm rabbits to 0.71 +/- 0.05, a value significantly higher than found for the surfactant used for treatment (0.55 +/- 0.04) (p < 0.05). The minimal surface tensions of large aggregate surfactant and the surfactant used for treatment (0.1 mg lipid/ml) were evaluated for inhibition by plasma proteins. Surfactant from NMU-injured and surfactant-treated rabbits was more resistant to inhibition (minimal surface tension, 5.7 +/- 3.9 dyne/cm in the presence of 0.6 mg/ml plasma protein) than the surfactant used for treatment (19.7 +/- 0.8 dyne/cm). These results indicate that after exposure to the injured lung, the function of the surfactant used for treatment was enhanced and made less sensitive to plasma inhibition of the surface-tension-lowering properties of surfactant. These changes probably result from the association of endogenous surfactant components with exogenous surfactant.