title: Amino acid metabolism in the human fetus at term: leucine, valine, and methionine kinetics.
abstract: Human fetal metabolism is largely unexplored. Understanding how a healthy fetus achieves its fast growth rates could eventually play a pivotal role in improving future nutritional strategies for premature infants. To quantify specific fetal amino acid kinetics, eight healthy pregnant women received before elective cesarean section at term, continuous stable isotope infusions of the essential amino acids [1-13C,15N]leucine, [U-13C5]valine, and [1-13C]methionine. Umbilical blood was collected after birth and analyzed for enrichments and concentrations using mass spectrometry techniques. Fetuses showed considerable leucine, valine, and methionine uptake and high turnover rates. α-Ketoisocaproate, but not α-ketoisovalerate (the leucine and valine ketoacids, respectively), was transported at net rate from the fetus to the placenta. Especially, leucine and valine data suggested high oxidation rates, up to half of net uptake. This was supported by relatively low α-ketoisocaproate reamination rates to leucine. Our data suggest high protein breakdown and synthesis rates, comparable with, or even slightly higher than in premature infants. The relatively large uptakes of total leucine and valine carbon also suggest high fetal oxidation rates of these essential branched chain amino acids.
authors.affiliation: Department of Pediatrics, Erasmus MC-Sophia Children's Hospital, 3000 CB Rotterdam, The Netherlands.
authors.forename: Chris H P
authors.initials: CH
authors.lastname: van den Akker
authors.forename: Henk
authors.initials: H
authors.lastname: Schierbeek
authors.forename: Gardi
authors.initials: G
authors.lastname: Minderman
authors.forename: Andras
authors.initials: A
authors.lastname: Vermes
authors.forename: Ernst M
authors.initials: EM
authors.lastname: Schoonderwaldt
authors.forename: Johannes J
authors.initials: JJ
authors.lastname: Duvekot
authors.forename: Eric A P
authors.initials: EA
authors.lastname: Steegers
authors.forename: Johannes B
authors.initials: JB
authors.lastname: van Goudoever
mesh_terms: D001783:Blood Flow Velocity; D002247:Carbon Isotopes / Q000378:metabolism; D005260:Female; D005312:Fetal Blood / Q000378:metabolism; D005333:Fetus / Q000378:metabolism*; D045782:Hemiterpenes; D006801:Humans; D007651:Keto Acids / Q000378:metabolism; D007700:Kinetics; D007930:Leucine / Q000008:administration & dosage / Q000097:blood*; D013058:Mass Spectrometry; D008431:Maternal-Fetal Exchange / Q000502:physiology*; D008715:Methionine / Q000008:administration & dosage / Q000097:blood*; D009587:Nitrogen Isotopes / Q000378:metabolism; D011247:Pregnancy; D018709:Statistics, Nonparametric; D014633:Valine / Q000008:administration & dosage / Q000097:blood*
chemical_list: D002247:Carbon Isotopes; D045782:Hemiterpenes; D007651:Keto Acids; D009587:Nitrogen Isotopes; C001505:alpha-ketoisovalerate; C013082:alpha-ketoisocaproic acid; D008715:Methionine; D007930:Leucine; D014633:Valine