Glycogen in liver may be synthesized either directly from glucose or indirectly from lactate and alanine, which are cleavage products of glucose in nonhepatic tissues and which are returned to liver. We are developing methods to measure the contribution of these pathways to glycogen in the intact animal (rat) by using radioactive and nonradioactive tracers. The radioactive tracer used here is water labeled with tritium (3HOH). The incorporation of labeled hydrogen on carbons 2 and 6 of glucose provides an estimate of these pathways that is much more reliable than with 14C labeled substrates. Another method to measure the pathways of glycogen is by using nonradioactive carbon (13C). Glucose labeled uniformly with 13C (U-13C) will be infused intragastrically in rats. Liver glycogen will be isolated and assayed by gas liquid-mass spectroscopy to obtain the distribution of masses from 181 to 186 (1 to 6 labeled carbons per molecule). The ratio of glucose of mass 186 to that of all labeled molecules provides an estimation of the direct pathway. This method also does not depend on the specific activity of precursors and attainment of steady state. The use of labeled substrates and mass spectroscopy to study glycogen and glucose synthesis and the operation of the Krebs cycle will be explored. The value of the use of nonradioactive tracers such as 13C is that ultimately these procedures can be applied to humans without risks due to radioaction damage.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Project (R01)
Project #
5R01DK036449-07
Application #
3234854
Study Section
Metabolism Study Section (MET)
Project Start
1985-12-15
Project End
1993-11-30
Budget Start
1991-12-01
Budget End
1992-11-30
Support Year
7
Fiscal Year
1992
Total Cost
Indirect Cost
Name
Cedars-Sinai Medical Center
Department
Type
DUNS #
075307785
City
Los Angeles
State
CA
Country
United States
Zip Code
90048
Wals, P A; Katz, J (1994) Glucose-glucose 6-phosphate cycling in hepatocytes determined by incorporation of 3HOH and D2O. Effect of glycosyns and fructose. J Biol Chem 269:18343-52
Katz, J; Wals, P; Lee, W N (1993) Isotopomer studies of gluconeogenesis and the Krebs cycle with 13C-labeled lactate. J Biol Chem 268:25509-21
Wals, P A; Katz, J (1993) A concentration gradient of glucose from liver to plasma. Metabolism 42:1492-6
Wals, P A; Katz, J (1993) The effect of D2O on glycolysis by rat hepatocytes. Int J Biochem 25:1561-4
Guo, Z K; Wals, P A; Katz, J (1991) Stimulation of glycogen synthesis by proglycosyn (LY177507) by isolated hepatocytes of normal and streptozotocin diabetic rats. J Biol Chem 266:22323-7
Lee, W N; Sorou, S; Bergner, E A (1991) Glucose isotope, carbon recycling, and gluconeogenesis using [U-13C]glucose and mass isotopomer analysis. Biochem Med Metab Biol 45:298-309
Lahtela, J T; Wals, P A; Katz, J (1990) Glucose metabolism and recycling by hepatocytes of OB/OB and ob/ob mice. Am J Physiol 259:E389-96
Katz, J (1989) The determination of mass of metabolites with tracers. Metabolism 38:728-33
Katz, J; Lee, W N; Wals, P A et al. (1989) Studies of glycogen synthesis and the Krebs cycle by mass isotopomer analysis with [U-13C]glucose in rats. J Biol Chem 264:12994-3004
Katz, J; Wolfe, R R (1988) On the measurement of lactate turnover in humans. Metabolism 37:1078-80

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