Gluconeogenesis measured with [u-13c]glucose and mass isotopomer
analysis of apolipoprotein b-100 amino acids in pigs.
Wykes, Linda J., Farook Jahoor, and Peter J. Reeds.
USDA/ARS Children's Nutrition Research Center, Department of
Pediatrics, Baylor College of Medicine, Houston TX, 77030. School of
Dietetics and Human Nutrition, McGill University, St Anne de
Bellevue, Canada.
APStracts 4:0228E, 1997.
Infant pigs (8.5 kg) were fasted for 16 h and infused for 6 h with [U
-13C]glucose. The fractional abundances of all 13C-mass isotopomers of
plasma glucose, lactate, pyruvate and of plasma, hepatic and VLDL
apolipoprotein B-100 (apoB-100) alanine, glutamate and aspartate were
measured. The ratios of [13C3]aspartate, [13C3]glutamate and
[13C3]alanine in apoB-100 were used to estimate the positional
equilibrium of [13C3]oxaloacetate, the fractional contribution of
pyruvate carboxylase to the hepatic oxaloacetate flux and the
activity of hepatic pyruvate dehydrogenase. The values were compared
with those based on glucose labeling and previously published
equations. The two methods gave similar estimates of the positional
equilibrium of [13C3] oxaloacetate (0.59, Katz; 0.61, apoB) but
slightly different estimates of the contribution of pyruvate
carboxylase to the oxaloacetate flux (0.36, Katz; 0.31 apoB).
Gluconeogenesis apparently contributed between 71 (Katz & Lee) and 80
(apoB) percent of the glucose entry rate (25 [mu]mol/kg/min) and
pyruvate dehydrogenase contributed 20% of the hepatic acetyl CoA. We
conclude that the labeling of aspartate in apoB-100 provides a good
estimate of the isotopomer distribution in hepatic oxaloacetate, but
may underestimate the absolute isotopic enrichment by 50%.
Received 7 March 1997; accepted in final form 8 October 1997.
APS Manuscript Number E104-7.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 29 October 1997