title: System A amino acid transporter activity in term placenta is substrate specific and inversely related to amino acid concentration.
abstract: Using intact villous fragments from normal term placentas, the authors characterize the effect of reduced amino acid availability on amino acid uptake via the system A amino acid transporter. Villous fragments deprived of amino acids demonstrate increased system A activity compared with those incubated in an amino acid-sufficient medium (P < .05). Similarly, placental villous fragments exposed to media containing only amino acids not specifically transported by system A have a significant increase in system A activity compared with villous fragments incubated in an amino acid-sufficient medium containing only substrates of system A (P < .05). There is a significant trend for increasing system A activity as the concentrations of the system A amino acid substrates are decreased (P < .01). Collectively, these data indicate that normal placentas can increase system A amino acid transporter activity in a substrate-specific and dose-dependent manner as a means to ensure optimal fetal growth in the presence of amino acid limitation.
authors.affiliation: Magee-Womens Research Institute, Department of Obstetrics and Gynecology and Reproductive Sciences, University of Pittsburgh, Pittsburgh, Pennsylania 15213, USA. parrott.meredith@medstudent.pitt.edu
authors.forename: Meredith Snook
authors.initials: MS
authors.lastname: Parrott
authors.forename: Frauke
authors.initials: F
authors.lastname: von Versen-Hoeynck
authors.forename: Roberta B
authors.initials: RB
authors.lastname: Ness
authors.forename: Nina
authors.initials: N
authors.lastname: Markovic
authors.forename: James M
authors.initials: JM
authors.lastname: Roberts
mesh_terms: D026924:Amino Acid Transport System A / Q000378:metabolism*; D000596:Amino Acids / Q000378:metabolism*; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D009752:Nutritional Status; D010920:Placenta / Q000378:metabolism*; D011247:Pregnancy; D013379:Substrate Specificity
chemical_list: D026924:Amino Acid Transport System A; D000596:Amino Acids