Bell A W, Kennaugh J M, Battaglia F C, Meschia G
Department of Pediatrics, University of Colorado School of Medicine, Denver 80262.
Q J Exp Physiol. 1989 Sep;74(5):635-43. doi: 10.1113/expphysiol.1989.sp003316.
Fetal uptakes of amino acids and ammonia via the umbilical circulation were measured in single pregnant ewes at mid-gestation (range 66-81 days). There were significant net fluxes from placenta to fetus of ammonia and twelve amino acids (in decreasing order: glutamine, glycine, alanine, proline, lysine, arginine, threonine, valine, leucine, tyrosine, asparagine, isoleucine) and net fluxes from fetus to placenta of glutamate and serine. The estimated serine flux was 139 mumol day-1 (g fetal dry wt)-1. Comparison with late gestation data indicated a similar pattern of amino acid exchange. However, the relatively large placental uptake of fetal serine was a distinctive feature of mid-gestation. The net fetal uptake of amino acid nitrogen was 2.83 +/- 0.66 micrograms N (mumol O2 uptake)-1, or 18 mg N day-1 (g dry wt)-1. This uptake was similar in magnitude to the combined fetal requirements for nitrogen accretion and urea synthesis and represented approximately 32 and 43% of fetal carbon and energy requirements, respectively.
