title: Partitioning of glutamine synthesised by the isolated perfused human placenta between the maternal and fetal circulations.
abstract: BACKGROUND
  Placental glutamine synthesis has been demonstrated in animals and is thought to increase the availability of this metabolically important amino acid to the fetus. Glutamine is of fundamental importance for cellular replication, cellular function and inter-organ nitrogen transfer. The objective of this study was to investigate the role of glutamate/glutamine metabolism by the isolated perfused human placenta in the provision of glutamine to the fetus.
  
  
  METHODS
  Glutamate metabolism was investigated in the isolated dually perfused human placental cotyledon. U-¹³C-glutamate was used to investigate the movement of carbon and ¹⁵N-leucine to study movement of amino-nitrogen. Labelled amino acids were perfused via maternal or fetal arteries at defined flow rates. The enrichment and concentration of amino acids in the maternal and fetal veins were measured following 5 h of perfusion.
  
  
  RESULTS
  Glutamate taken up from the maternal and fetal circulations was primarily converted into glutamine the majority of which was released into the maternal circulation. The glutamine transporter SNAT5 was localised to the maternal-facing membrane of the syncytiotrophoblast. Enrichment of ¹³C or ¹⁵N glutamine in placental tissue was lower than in either the maternal or fetal circulation, suggesting metabolic compartmentalisation within the syncytiotrophoblast.
  
  
  CONCLUSIONS
  Placental glutamine synthesis may help ensure the placenta's ability to supply this amino acid to the fetus does not become limiting to fetal growth. Glutamine synthesis may also influence placental transport of other amino acids, metabolism, nitrogen flux and cellular regulation.
  
  
  CONCLUSIONS
  Placental glutamine synthesis may therefore be a central mechanism in ensuring that the human fetus receives adequate nutrition and is able to maintain growth.
authors.affiliation: University of Southampton, Faculty of Medicine, Human Development and Health, United Kingdom.
authors.forename: P E L
authors.initials: PE
authors.lastname: Day
authors.forename: J K
authors.initials: JK
authors.lastname: Cleal
authors.forename: E M
authors.initials: EM
authors.lastname: Lofthouse
authors.forename: V
authors.initials: V
authors.lastname: Goss
authors.forename: G
authors.initials: G
authors.lastname: Koster
authors.forename: A
authors.initials: A
authors.lastname: Postle
authors.forename: J M
authors.initials: JM
authors.lastname: Jackson
authors.forename: M A
authors.initials: MA
authors.lastname: Hanson
authors.forename: A A
authors.initials: AA
authors.lastname: Jackson
authors.forename: R M
authors.initials: RM
authors.lastname: Lewis
mesh_terms: D026921:Amino Acid Transport Systems, Neutral / Q000378:metabolism; D001692:Biological Transport; D002247:Carbon Isotopes; D002462:Cell Membrane / Q000378:metabolism; D005260:Female; D047109:Fetal Development; D018698:Glutamic Acid / Q000378:metabolism; D005973:Glutamine / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D007930:Leucine / Q000378:metabolism; D008431:Maternal-Fetal Exchange; D008954:Models, Biological; D009587:Nitrogen Isotopes; D010477:Perfusion; D010920:Placenta / Q000098:blood supply / Q000166:cytology / Q000378:metabolism*; D021041:Placental Circulation; D011247:Pregnancy; D014327:Trophoblasts / Q000166:cytology / Q000378:metabolism
chemical_list: D026921:Amino Acid Transport Systems, Neutral; D002247:Carbon Isotopes; D009587:Nitrogen Isotopes; C424137:SLC38A5 protein, human; D005973:Glutamine; D018698:Glutamic Acid; D007930:Leucine
keywords: Amino acid; Glutamate; Glutamine; Metabolism; System N