Lung surfactant kinetics in conscious pigs.

The primary goal of this study was to determine the contributions of plasma free fatty acids (FFA) and de novo synthesized fatty acids (FA) to lung surfactant phosphatidylcholine (PC) synthesis. A new stable isotope tracer model was developed in which [1,2-13C2]acetate and uniformly labeled [U-13C16]palmitate were infused in nine normal overnight fasted pigs to quantify surfactant kinetics in the basal state and during low-dose glucose infusion (2 mg ⋅ kg-1 ⋅ min-1). There was no effect of glucose; therefore, all data were pooled. The surfactant PC-bound palmitate incorporation rate from plasma palmitate was 20.9 ± 1.9 nmol palmitate ⋅ h-1 ⋅ g wet lung-1, compared with the rate of 2.1 ± 0.3 nmol palmitate ⋅ h-1 ⋅ g wet lung-1 from de novo synthesized palmitate. The PC-bound palmitate secretion rate from the lamellar body pool to the alveolar surface pool was 239 ± 26 nmol palmitate ⋅ h-1 ⋅ g wet lung-1. Approximately 90% of the secreted PC recycled back to the lamellar bodies for reutilization. We conclude that plasma is the primary contributor of FA for surfactant PC synthesis under the conditions of this experiment.