Separation and partial characterization of surface-active fractions from mouse and rat lung homogenates. Identification of a possible marker system for pulmonary surfactant.

The purpose of this study was to identify a "marker system" for pulmonary surfactant. A density gradient centrifugation procedure was developed to concentrate the surface-active material in mouse and rat lung homogenates. These fractions contained morphologic variants of surfactant such as lamellar bodies and tubular myelin. Lipid and protein analyses were consistent with other techniques indicating that these preparations were surface active. A comparison of the nonspecific esterases in these and other surfact-active preparations (i.e., pulmonary lavage fluid and isolated type II cells) allowed the identification of certain surfactant-associated esterases which are distinguishable electrophoretically and cytochemically from the other pulmonary esterases and which, therefore, may be used as "markers" for surfactant. Possible uses for these enzyme markers in studies of (a) the sites of synthesis and routes of clearance of surfactant and (b) the assessment of variations in surface activity due to either diseases such as the respiratory distress syndrome or to experimental manipulation are discussed.