title: Placental and fetal serine fluxes at midgestation in the fetal lamb.
abstract: Plasma serine disposal rate (DR), decarboxylation, and conversion to fetal plasma glycine by the placenta were measured in six fetal lambs at 72 +/- 1 days gestation. L-[1-13C]serine, L-[U-14C]serine, and 3H2O were infused over 3 h into the fetal circulation, the latter for measurement of uterine and umbilical blood flow. The fetal plasma serine DR was 8.7 +/- 1.0 mumol/min or 61.8 +/- 4 mumol.min-1.kg fetus-1. Approximately 90% of the DR represented placental uptake of fetal serine. There was no detectable release of fetal serine into the maternal circulation. The fetal arterial plasma glycine-to-serine enrichment ratio was approximately 0.30. The conversion rate of fetal serine to fetal plasma glycine by the placenta was 5.8 +/- 0.7% of the serine DR. Fetal and placental CO2 production from fetal plasma serine carbon was 1.9 +/- 0.4 and 1.2 +/- 0.4 mumol/min, respectively. Thus, at midgestation, there is a rapid fetoplacental serine exchange that constitutes most of the fetal plasma serine turnover. Placental conversion of serine to fetal glycine and serine oxidation together account for only 10% of the placental uptake of fetal serine.
authors.affiliation: Department of Pediatrics, University of Colorado School of Medicine, Denver 80262.
authors.forename: R R
authors.initials: RR
authors.lastname: Moores
authors.forename: B S
authors.initials: BS
authors.lastname: Carter
authors.forename: G
authors.initials: G
authors.lastname: Meschia
authors.forename: P V
authors.initials: PV
authors.lastname: Fennessey
authors.forename: F C
authors.initials: FC
authors.lastname: Battaglia
mesh_terms: D000818:Animals; D002245:Carbon Dioxide / Q000378:metabolism; D005260:Female; D005312:Fetal Blood / Q000378:metabolism*; D005333:Fetus / Q000378:metabolism; D005865:Gestational Age; D005998:Glycine / Q000097:blood; D009994:Osmolar Concentration; D010920:Placenta / Q000378:metabolism*; D011247:Pregnancy; D012694:Serine / Q000097:blood / Q000378:metabolism*; D012756:Sheep
chemical_list: D002245:Carbon Dioxide; D012694:Serine; D005998:Glycine