Isolation and surface activity of soluble alveolar components

Abstract

Fractional alveolar lavage from normal rabbits, in which pulmonary capillary blood is replaced by a non-wetting fluorocarbon contains little protein, but does contain large amounts of lipid. This lipid is 92% lecithin, most of which is saturated. Lavage from rabbits in which pulmonary capillary blood is present contains 70% lipid and 30% protein. This protein is electrophoretically identified to serum albumin. This lipid contains large amounts of unsaturated lecithins and fatty acids. The isolated saturated lecithin from lavage exhibits essentially zero surface tension upon compression, as does lavage fluid obtained from bloodless lungs. Addition of palmitic acid to the lecithin results in markedly higher minimum surface tension. Addition of various proteins “stabilizes” the lecithin monolayer against repeated compression, but in contrast to fatty acids does not prevent achievement of zero surface tension upon compression. These studies suggest that the alveolus is normally lined with saturated lecithin, essentially free of other lipids, protein or carbohydrate.