Because minimal information is available about
surfactant metabolism in
bronchopulmonary dysplasia, we measured half-lives and pool sizes of
surfactant phosphatidylcholine in very preterm baboons recovering from
respiratory distress syndrome and developing
bronchopulmonary dysplasia, using stable
isotopes, radioactive isotopes, and direct pool size measurements. Eight ventilated premature baboons received (2)H-DPPC (
dipalmitoyl phosphatidylcholine) on d 5 of life, and radioactive (14)C-DPPC with a treatment dose of
surfactant on d 8. After 14 d, lung pool sizes of saturated
phosphatidylcholine were measured. Half-life of (2)H-DPPC (d 5) in tracheal aspirates was 28 +/- 4 h (mean +/- SEM). Half-life of radioactive DPPC (d 8) was 35 +/- 4 h. Saturated
phosphatidylcholine pool size measured with stable
isotopes on d 5 was 129 +/- 14 micro mol/kg, and 123 +/- 11 micro mol/kg on d 14 at autopsy. Half-lives were comparable to those obtained at d 0 and d 6 in our previous baboon studies. We conclude that
surfactant metabolism does not change during the early development of
bronchopulmonary dysplasia, more specifically, the metabolism of exogenous
surfactant on d 8 is similar to that on the day of birth.
Surfactant pool size is low at birth, increases after
surfactant therapy, and is kept constant during the first 2 wk of life by endogenous
surfactant synthesis. Measurements with stable
isotopes are comparable to measurements with
radioactive tracers and measurements at autopsy.