title: The effect of an elevated maternal lysine concentration on placental lysine transport in pregnant sheep.
abstract: OBJECTIVE
  In a previous study, the coinfusion into the maternal circulation of lysine and several other amino acids failed to increase significantly lysine umbilical uptake. The purpose of this study was to determine whether umbilical lysine uptake can be increased by infusing a lysine solution that does not contain any other amino acid.
  
  
  METHODS
  Six late-gestation ewes were studied on 2 consecutive days. Samples were collected in both the control (first day) and experimental (second day) periods simultaneously from the maternal artery, uterine vein, fetal artery, and umbilical vein. In the control period, L-[1-(13)C] lysine was infused into the maternal circulation. During the experimental period, both L-[1-(13)C] lysine and L-(12)C lysine were infused to increase maternal lysine concentration. Uterine and umbilical blood flows were measured by the steady state diffusion technique. Uterine and umbilical uptake of lysine and of alpha-aminoaminoadipic acid (AAD, a biproduct of lysine oxidation) were calculated.
  
  
  RESULTS
  In response to a 2.7-fold increase in maternal lysine concentration (P<.001), fetal lysine concentration increased approximately 70% (P<.05) and umbilical uptake 50% (P<.05). In the experimental period, there was a significant (P<.05) placental uptake of fetal AAD, and the fetal/maternal plasma (13)C-lysine-specific activity ratio increased from 0.221+/-0.026 to 0.294+/-0.029 (P<.05). In response to the increase in maternal lysine concentration, the maternal and fetal concentrations of several other amino acids were significantly decreased.
  
  
  CONCLUSIONS
  This study establishes that the umbilical uptake of lysine can be increased by infusing lysine in the maternal circulation. However, the lysine infusion is associated with a decrease in the maternal concentration and umbilical uptake of other essential amino acids. These data, compared with the results of previous studies, indicate that attempts to increase the fetal uptake of an amino acid via maternal infusion may decrease the uptake of other amino acids by decreasing their maternal concentration and by inhibition of placental transport.
authors.affiliation: Department of Obstetrics and Gynecology, University of Colorado Health Sciences Center, Denver, CO, USA.
authors.forename: Paul T
authors.initials: PT
authors.lastname: Wilkes
authors.forename: Giacomo
authors.initials: G
authors.lastname: Meschia
authors.forename: Cecilia
authors.initials: C
authors.lastname: Teng
authors.forename: Yaming
authors.initials: Y
authors.lastname: Zhu
authors.forename: Randall B
authors.initials: RB
authors.lastname: Wilkening
authors.forename: Frederick C
authors.initials: FC
authors.lastname: Battaglia
mesh_terms: D015074:2-Aminoadipic Acid / Q000097:blood / Q000378:metabolism; D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D005260:Female; D005312:Fetal Blood; D005333:Fetus / Q000378:metabolism; D008239:Lysine / Q000097:blood / Q000493:pharmacokinetics*; D009994:Osmolar Concentration; D010920:Placenta / Q000378:metabolism*; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000097:blood / Q000378:metabolism*; D012756:Sheep
chemical_list: D000596:Amino Acids; D015074:2-Aminoadipic Acid; D008239:Lysine