Use of the labeling pattern of liver glutamate to calculate rates
of krebs cycle and gluconeogenesis.
Large, Val[acute]erie, Henri Brunengraber, Mich[grave]ele Odeon, and
Michel Beylot.
INSERM U. 197, Lyon, France and Department of Nutrition, C.W.R.U.,
Cleveland, USA
APStracts 3:0195E, 1996.
It has been proposed to use the labeling pattern of hepatic glutamate
during infusion of L[3-13C] or [3-14C]lactate in order to calculate
rates of Krebs cycle activity and gluconeogenesis. We tested the
validity of this approach by perfusing isolated rat livers (48h
starved) with pyruvate + lactate (10 % enriched with [3-13C]lactate)
without (control) or with infusion of glucagon (to inhibit pyruvate
kinase), mercaptopicolinate (to inhibit phosphoenol-pyruvate
carboxykinase) or dichloroacetate (to stimulate pyruvate
dehydrogenase). Compared to control experiments glucagon increased
glucose output (p<0.05) and decreased the calculated flux
through pyruvate kinase (p<0.05). Mercaptopicolinate
suppressed almost totally glucose production and reduced dramatically
the calculated gluconeogenic rate and flux through
phosphoenolpyruvate carboxy-kinase (p<0.001). Dichloroacetate
increased moderately the calculated flux through pyruvate
dehydrogenase (p<0.05). In experiments with perfused livers
from fed rats, the calculated gluconeogenic rate and flux through
phosphoenolpyruvate carboxykinase were very low compared to control
experiments (p<0.001) whereas the pyruvate dehydrogenase flux
was increased (p<0.05). Therefore the expected modifications
of Krebs cycle activity and gluconeogenic rate were clearly detected
using the labeling pattern of glutamate and the model proposed by
Magnusson et al. Except for the perfusions with mercaptopicolinate,
the dilution by isotopic exchange in the oxaloacetate pool calculated
from the model agreed with the actual dilution of enrichment between
liver pyruvate and phosphoenolpyruvate. The present results support
the validity of this approach to trace liver metabolism.
Received 15 April 1996; accepted in final form 21 August 1996.
APS Manuscript Number E193-5.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 7 October 1996