AJP - Endocrinology and Metabolism, Vol 264, Issue 2 E221-E225, Copyright © 1993 by American Physiological Society
Ovine fetal placental lactate exchange and decarboxylation at midgestation
B. S. Carter, R. R. Moores Jr, F. C. Battaglia and G. Meschia
Department of Pediatrics, University of Colorado School of Medicine, Denver 80262.
In a study of the metabolic implications of the large placental-to-fetal
mass ratio that characterizes early fetal development, fetal plasma lactate
disposal rate and CO2 production from fetal plasma lactate by fetus and
placenta were measured in six midgestation (71-80 days) pregnant sheep. A
constant fetal intravenous infusion of L-[U-14C]lactate and 3H2O was given
to establish fetal steady-state lactate specific activity and to measure
uterine and umbilical blood flows. Fetal and placental weights were 158.6
+/- 19.7 and 441.9 +/- 32.7 g, respectively. There was a significant net
lactate flux into the uterine circulation (31 +/- 4.3 mumol/min, P <
0.01) but no measurable umbilical uptake. Fetal plasma lactate disposal
rate was 21.2 +/- 2.7 mumol/min, approximately one-half of which
represented fetal lactate flux into the placenta (9.9 +/- 1.9 mumol/min).
The oxidation rate of tracer lactate carbon to 14CO2 by placenta plus fetus
was 72.6 +/- 4.7% of the infused tracer and was fairly evenly distributed
between the placenta and the fetus (42.4 +/- 3.9 vs. 30.3 +/- 2.2%). The
midgestation placenta metabolizes and produces fetal plasma lactate at
rapid and nearly equal rates. This contrasts with the late-gestation
placenta, which makes a small contribution to fetal lactate disposal and is
a major net source of fetal lactate.
