The labeling of pulmonary surfactant phosphatidylcholine in newborn and adult sheep.

The labeling of the saturated phosphatidylcholine from surfactant with radiolabeled palmitic acid was characterized in seven newborn and seven adult sheep using a repetitive sampling technique. Each animal had a small cannula placed surgically in the trachea. Following the intravenous injection of (3H) palmitic acid, surfactant samples in saline were recovered from the distal airways of each animal with fine plastic catheters over a period of 10 days. The change in specific activity of the saturated phosphatidylcholine (cpm/mumol) was used to define the kinetics of secretion and then disappearance of the labeled saturated phosphatidylcholine. Labeled saturated phosphatidylcholine accumulated in a linear fashion without an apparent initial delay for 27 hr in adult and 44 hr in newborn sheep. The labeled saturated phosphatidylcholine then decayed with mean apparent biological half-life values of 45 hr and 54 hr in adult and newborn sheep, respectively. However, these half-life estimates are compromised by the long secretory phase of the labeling curves. The characteristics of the labeling of surfactant saturated phosphatidylcholine in sheep may be more representative of surfactant metabolism in large mammals than previous studies in small rodents.