Metabolism of endogenous surfactant in premature baboons and effect of prenatal corticosteroids

We studied the synthesis of surfactant and the effect of prenatal betamethasone treatment in vivo in very preterm baboons. Ten pregnant baboons were randomized to receive either betamethasone (beta) or saline (control) 48 and 24 h before preterm delivery. The newborn baboons were intubated, treated with surfactant, and ventilated for 6 d. They received a 24-h infusion with the stable isotope [U-(13)C]glucose as precursor for the synthesis of palmitic acid in surfactant phosphatidylcholine (PC). Palmitic acid in surfactant PC became enriched 27 +/- 2 h after the start of the isotope infusion and was maximally enriched at 100 +/- 4 h. The fractional synthesis rate of PC palmitate in the beta group (1.5 +/- 0.2%/d) was increased by 129% above control (0.7 +/- 0.1%/d) (p < 0.02, Mann- Whitney U test). The absolute synthesis rate of PC in the beta group [1.6 +/- 0.3 micromol/kg/d] was increased by 128% above controls [0.7 +/- 0.2 micromol/kg/d] (p < 0.02). These data show that the synthesis of endogenous surfactant from plasma glucose as precursor is a slow process. It is shown, for the first time in vivo, that prenatal glucocorticosteroids stimulate the synthesis of surfactant PC in the very premature baboon

Endogenous surfactant turnover in preterm infants measured with stable isotopes

We studied surfactant synthesis and turnover in vivo in preterm infants using the stable isotope [U-13C]glucose, as a precursor for the synthesis of palmitic acid in surfactant phosphatidylcholine (PC). Six preterm infants (birth weight, 916 +/- 244 g; gestational age, 27.7 +/- 1.7 wk) received a 24-h [U-13C]glucose infusion on the first day of life. The 13C-enrichment of palmitic acid in surfactant PC, obtained from tracheal aspirates, was measured by gas chromatography-combustion interface-isotope ratio mass spectrometry. We observed a significant incorporation of carbon-13 from glucose into surfactant PC palmitate. PC palmitate became enriched after 19.4 +/- 2.3 (16.5 to 22.3) h and reached 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 absolute production rate of surfactant PC to be 4.2 mg/kg/d, and the half-life to be 113 +/- 25 (87 to 144) h. Data on endogenous surfactant production and turnover were obtained for the first time in human infants with the use of stable isotopes. This novel and safe method could be applied to address many important issues concerning surfactant metabolism in preterm infants, children, and adults