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Six 120-day and 6 130-day gestational age lambs were delivered by C-section and supported on ventilators with 100% oxygen. With respiratory failure (pCO2=114±11) the lambs were treated with
50 mg/kg of 3H labeled NS by tracheal instillation. All the lambs responded dramatically, however the effect was gone within 3 hrs. The specific activity of the 3H labeled saturated
phosphatidyl choline (SPC) in the NS used for treatment had decreased by only 30±4% in the alveolar wash (AW) at sacrifice; thus the treatment dose was minimally diluted. However, IV
injections of 14C-palmitic acid resulted in the appearance of 14C-SPC in sequential samples suctioned from the airways (AS) indicating endogenous synthesis and secretion. Minimum surface
tension (ST) measurements (dynes/cm) made on AS fell from 29±2 to 8±5 after NS and again rose to 32±2 at sacrifice. AW samples taken at sacrifice and containing 1μmole phosphatidylcholine
(PC) did not lower ST below 27±4, while “surfactant” recovered from the AW (R-SA) containing 0.2 μmoles PC lowered ST to
