http://repub.eur.nl/res/aut/13455/ List of Publications en http://repub.eur.nl/static-eur/img/logo.png http://repub.eur.nl http://repub.eur.nl/res/pub/23543/ 2001-10-24T00:00:00Z During pregnancy, the fetus receives from its mother a continuous intravenous supply of energy substrates via the placenta. In most species, plasma lipids do not readily cross the placenta. In the human, where the placental transfer oflipids is limited, these substrates do not contribute to fetal oxidative metabolism since fetal tissues have a very low capacity for free fatty acids (FFA) oxidation. The FFA that cross the placenta are stored in adipose tissue and liver. 'When the mother is well fed, the supply of glucose and amino acids to the fetus is sufficient to cover its needs for oxidative metabolism and growth, and the fetus has no need to produce endogenous glucose. Excess of glucose is stored as glycogen in many tissues, particularly in the liver and as lipids in adipose tissue. After birth, the continuous intravenous high-carbohydrate low-fat diet ofthe fetus is replaced by a discontinuous enteral high-fat lowcarbohydrate diet. http://repub.eur.nl/res/pub/8795/ 1998-01-01T00:00:00Z 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.