Estimation of liver glucose metabolism after refeeding
Refeeding or infusing glucose to rats fasted for 24 hr or more causes rapid liver glycogen synthesis, the carbon source now considered to be largely from gluconeogenesis. While substrate cycling between plasma glucose and liver glucose-6P is known to occur, this cycling has apparently been ignored when calculations are made of % contribution of direct and indirect pathways to liver glycogen synthesis, or when hepatic glucose output is calculated from glucose turnover minus the glucose infusion rate. They show that, isotopically, an estimate of the fluxes of liver glucokinase and glucose-6-phosphatase is required to quantitate sources of carbon for liver glycogen synthesis, and to measure hepatic glucose output (or uptake). They propose a method to estimate these fluxes, involving a short infusion of a /sup 14/C labelled gluconeogenic precursor plus (6T)glucose, with determination of isotopic yields in liver glycogen and total glucose. Given also the rate of liver glycogen synthesis, this procedure permits the estimation of net gluconeogenesis and hepatic glucose output or uptake. Also, in vitro evidence against the notion of a drastic zonation of liver carbohydrate metabolism is presented, e.g. raising the glucose concentration from 10 to 25 mM increases the /sup 14/C yield from H/sup 14/CO/sub 3//sup -/ in lactate, with the increased pyruvate kinase flux and decreased gluconeogenesis occurring in the same cell type, not opposing pathways in different hepatocyte types (as has been postulated by some to occur in vivo after refeeding.
- Research Organization:
- Lemontree Research Institute, Sylmar, CA
- OSTI ID:
- 6071599
- Report Number(s):
- CONF-870644-
- Journal Information:
- Fed. Proc., Fed. Am. Soc. Exp. Biol.; (United States), Journal Name: Fed. Proc., Fed. Am. Soc. Exp. Biol.; (United States) Vol. 46:6; ISSN FEPRA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
59 BASIC BIOLOGICAL SCIENCES
ALDEHYDES
ANIMALS
BIOLOGICAL PATHWAYS
BODY
CARBOHYDRATES
CARBON 14 COMPOUNDS
DIGESTIVE SYSTEM
ENZYME ACTIVITY
ENZYMES
ESTERASES
GLANDS
GLUCOSE
HEXOSES
HYDROLASES
ISOTOPE APPLICATIONS
LABELLED COMPOUNDS
LIVER
MAMMALS
METABOLISM
MONOSACCHARIDES
ORGANIC COMPOUNDS
ORGANS
PHOSPHATASES
PHOSPHORUS-GROUP TRANSFERASES
PHOSPHOTRANSFERASES
RATS
RODENTS
SACCHARIDES
TRACER TECHNIQUES
TRANSFERASES
VERTEBRATES