In vivo clearance of natural and modified surfactant.

The loss of radiolabelled phosphatidylcholine associated with surfactants and lipid extracts of surfactants from different species sources was measured following tracheal injection into the lungs of adult and 3 day old rabbits. Clearance was more rapid from the lungs of adult than 3 day old rabbits. The percent labelled phosphatidylcholine cleared per 24 h did not change independently of dose injected indicating that clearance and catabolic pathways were not saturable in either group of rabbits. Different species sources or lipid extraction of natural surfactants did not alter clearance rates very much in the 3 day old rabbits. Small differences in clearance rates were identified by comparing rabbit surfactant with calf surfactant or Surfactant-TA in the adult rabbits. These results indicate that the lungs of developing and adult rabbits can clear large doses of surfactants from multiple sources at rates comparable to the species common natural surfactant.