Clearance of treatment doses of surfactant. Effect of lipid extraction and aggregate sizes.

Three-day-old rabbits were given intratracheal injections with a variety of surfactants at doses of about 100 mg lipid/kg, doses commonly used in clinical trials of surfactant for respiratory distress syndrome. Calf and sheep natural surfactants isolated by centrifugation of alveolar washes were compared with Surfactant-TA and two aggregate sizes of lipid solvent extracted sheep surfactant by measuring the percent recoveries of labeled phosphatidylcholine in alveolar washes and lung tissue at times to 48 h after surfactant injection. Surfactant-TA and the lipid extracted surfactants did not contain the 28 to 35-kdalton surfactant protein. All surfactants had similar linear clearance rates from the total lung (alveolar wash plus lung tissue), independent of species source, extraction with lipid solvents, or aggregate sizes of the phospholipids in suspension. There were no metabolic consequences to lipid extraction, the loss of 28-35 kdaltons of protein, or changes in aggregate sizes of surfactant lipids when injected in treatment doses into the airways of 3-day-old rabbits.