1652 CRITERIA FOR EXOGENOUS SURFACTANTS:

Exogenously administered surfactant (SAM) should achieve the same surface activity (SA) as natural surfactants and meet additional criteria for rate of surface dispersion and bulk phase thermal properties. We used three methods for isolating SAM from tracheal lavage of adult rabbits: (1) simple centrifugation, (2) a single sucrose density gradient, and (3) multiple continuous/discontinuous density gradients (King/Clements). Standard amounts of SAM (30nM lipid phosphorous) were studied for surface activity and surface dispersion rates. SA criteria are minimum γ (dynes/cm); compressibility (cm/dyne); and surface areas at 12 dynes, and at first film collapse. SAM dispersion rates were defined as Δγ/sec. when SAM was applied to a 30cm2 surface area at 24°C. Scanning calorimetry defined the temperature of maximal melting (Tm,C°). No differences were found for the 3 methods in SA or disaturated phosphatidylcholine (DSPC)(μg/mg dry SAM). Protein content is greater in the least pure extract (p<.001). Crude (1) and pure (3) SAM were instilled in immature rabbits (27 days' gestation) with significant improvement in pulmonary deflation pressure volume relationships.