Glycine turnover and oxidation and hepatic serine synthesis from glycine in fetal lambs

I. Cetin, P. V. Fennessey, A. N. Quick, A. M. Marconi, G. Meschia, F. C. Battaglia, J. W. Sparks

Research output: Contribution to journalArticlepeer-review

56 Scopus citations


[1-13C]- and [1-14C]glycine were infused into chronically catheterized fetal lambs via a branchial vein. At tracer glycine steady state, samples were collected from the fetal abdominal aorta, umbilical vein, and fetal hepatic vein and from the maternal femoral artery and uterine vein. The samples were analyzed for plasma glycine and serine, for glycine and serine 13C atom% excess (APE), and for whole blood 14CO2 and O2 concentrations. Fetal plasma glycine disposal rate (DR) was 12.4 ± 0.8 μmol·min-1·kg fetus-1·CO2 production from decarboxylation of fetal plasma glycine was 1.63 ± 0.16 μmol·min-1·kg fetus-1 and represented 12.3 ± 0.7% of DR. Approximately 50% of infused tracer glycine was taken up by the fetal liver with the release of labeled serine and CO2 in the fetal circulation. There was no detectable efflux of tracer glycine from the placenta into the maternal circulation. The tracer production of serine and CO2 accounted for 23 and 17%, respectively, of the hepatic tracer glycine uptake. The labeled CO2 released by the liver was a large fraction (~70%) of the labeled CO2 produced by the fetus. The serine-to-glycine APE ratio in fetal plasma was ~5%. These results indicate that the fetal liver is the major site of fetal plasma glycine decarboxylation and of serine synthesis from plasma glycine.

Original languageEnglish (US)
Pages (from-to)E371-E378
JournalAmerican Journal of Physiology - Endocrinology and Metabolism
Issue number3 23-3
StatePublished - 1991
Externally publishedYes


  • Fetal hepatic glycine uptake
  • Fetal serine production
  • Placental glycine uptake
  • Stable isotopes
  • Umbilical glycine uptake

ASJC Scopus subject areas

  • Endocrinology, Diabetes and Metabolism
  • Physiology
  • Physiology (medical)


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