Incorporation of Labeled Palmitate into “Alveolar” and Whole Lung Phospholipids of Fetal and Newborn Lambs ∗

Summary

The incorporation of labeled palmitate into the phospholipid components of pulmonary surface-active material and whole lung tissue was studied in fetal and newborn lambs. Labeled palmitate was incorporated into the “alveolar” phospholipids. The radioactivity in the “alveolar” phosphatidylcholine was two to three times greater in lambs allowed to breathe for 10 min. In older newborn lambs, the activity was ten times greater than in the fetus.

The radioactivity and specific activity of the whole lung tissue phosphatidylcholine were similar in fetal and newborn lambs up to 2 days of age, at which time both decreased markedly. The radioactivity was evenly distributed between the alpha and beta positions of both the “alveolar” and whole lung tissue phosphatidylcholine

The radioactivity of the “alveolar” phosphatidylcholine constitutes only a small fraction of the whole-lung phosphatidylcholine. These results indicate that the surface-active material is synthesized in the fetal lung and secreted onto the alveolar space prior to birth, and is further discharged after the onset of respiration.