ENDOGENOUS SURFACTANT TURNOVER IN PRETERM INFANTS MEASURED WITH STABLE ISOTOPES

We studied surfactant synthesis and turnover in vivo in preterm infant s using the stable isotope [U-C-13]glucose, as a precursor for the syn thesis of palmitic acid in surfactant phosphatidylcholine (PC). Six pr eterm infants (birth weight, 916 +/- 244 g; gestational age, 27.7 +/- 1.7 wk) received a 24-h [U-C-13]glucose infusion on the first day of l ife. The C-13-enrichment of palmitic acid in surfactant PC, obtained f rom tracheal aspirates, was measured by gas chromatography-combustion interface-isotope ratio mass spectrometry. We observed a significant i ncorporation of carbon-13 from glucose into surfactant PC palmitate. P C palmitate became enriched after 19.4 +/- 2.3 (16.5 to 22.3) h and re ached maximum enrichment at 70 +/- 18 (48 to 96) h after the start of the label infusion. The fractional synthesis rate (FSR) of surfactant PC palmitate from glucose was 2.7 +/- 1.3%/d. We calculated the absolu te production rate of surfactant PC to be 4.2 mg/kg/d, and the half-li fe to be 113 +/- 25 (87 to 144) h. Data on endogenous surfactant produ ction and turnover were obtained for the first time in human infants w ith the use of stable isotopes. This novel and safe method could be ap plied to address many important issues concerning surfactant metabolis m in preterm infants, children, and adults.