Introduction
Metabolic Solutions offers project design assistance
and a mass spectrometry service to help researchers
study glucose metabolism using stable isotope methods.
The primed constant infusion of stable isotope labeled
glucose has been extensively validated as a reliable
approach to quantifying glucose kinetics. This approach
can be used to explore whole body glucose homeostasis
under various perturbations such as exogenous infusions
of glucose and insulin. Sensitive methods for measuring
labeled glucose in plasma have been developed to permit
quantification with 50-100 µl of plasma. Thus, these
studies can be performed relatively easy in newborns.
List of Glucose Metabolism Services:
- Endogenous production and flux measurements
- Cori cycling
- Oxidation
- Gluconeogenesis
- Kreb cycle kinetics
- Lactate and pyruvate kinetics
Glucose Production Rate
If a known amount of glucose is administered, then the
glucose production rate can be calculated. The following
protocol illustrates a method for measuring glucose production
rate:
Best Tracer: 6,6-D2-Glucose
Priming Bolus Dose:
14.0 µmol/kg
Infusion Pump Speed:
0.174 cc/min
Infusion Rate: 11.5
µmol/kg/hr
Infusion Time: 140 min.
Sampling Times: 0, 90,
100, 110, 120, 130, 140 min. (Plasma)
Diet Protocol: Fasted
or Fed
References: Bier et
al., Diabetes 26, 1005-1015,
1977
Bier
et al., Diabetes 26, 1016-1023,
1977
Shaw
and Wolfe, Surgery 97, 557-568,
1985
Glucose Recycling
Glucose and fructose recycling rates can be measured
in addition to glucose flux and production rate.
The measured rates of cycling in glycosis and gluconeogenesis
represents the total substrate cycling rates between
glucose and glucose-6-phosphate and fructose-6-phosphate
and fructose-1,6-diphosphate. The following
protocol illustrates a method for measuring glucose
recycling:
Best Tracer: 6,6-D2-Glucose
and 2-D1-Glucose
Priming Bolus Dose: 17.8 µmol/kg each
tracer
Infusion Pump Speed: 0.174 cc/min
Infusion Rate: 13.2 µmol/kg/hr
Infusion Time: 140 min.
Sampling Times: 0, 90, 100, 110, 120,
130, 140 min. (Plasma)
Diet Protocol: Fasted or Fed
References: Shulman et al., J. Clin.
Invest. 76, 757-764, 1985
Miyoshi
et al., J. Clin. Invest. 81, 1545-1555, 1988
Glucose Oxidation
The rate of glucose oxidation can be calculated using
a 13C-labeled glucose. Samples of
blood are collected to determine the plateau level
of 13C-blood while expired breath samples
are used to determine the enrichment of 13CO2.
The bicarbonate pool is primed with NaH13CO3.
The following protocol illustrates a method for measuring
glucose oxidation:
Best Tracer: U-(13C6)-glucose
Priming Bolus Dose: 1.1 µmol/kg U-(13C6)-glucose
Infusion Pump Speed: 0.174 cc/min
Infusion Rate: 2.5 µmol/kg/hr
Infusion Time: 140 min.
Sampling Times: 0, 90, 100, 110, 120,
130, 140 min. (Plasma and breath)
Diet Protocol: Fasted or Fed
References: Wolfe et al., Metabolism
28, 210-219, 1979.
Robert
et al., Diabetes 31, 203-211,
1982.
Glucose Synthesis from Precursors
The rate of gluconeogenesis can be quantified from
gluconeogenic substrates using 13C stable
isotope tracers. For example, to quantify the
glucose-alanine relationship, one needs to determine
the incorporation of alanine carbon into glucose.
In addition, the fraction of lactate produced from
alanine can be determined by measuring the enrichment
of lactate. These studies require the infusion
of [2,3-13C2]-alanine and 6,6-D2-glucose
as tracers. The following protocol illustrates
a method for measuring glucose synthesis from precursors:
Protocol
Best Tracer: [2,3-13C2]-alanine
and 6,6-D2-glucose
Priming Bolus Dose: 1.1 µmol/kg Each
Tracer
Infusion Pump Speed: 0.174 cc/min
Infusion Rate: 11.5 µmol/kg/hr
Infusion Time: 140 min.
Sampling Times: 0, 90, 100, 110, 120,
130, 140 min. (Plasma and breath)
Diet Protocol: Fasted or Fed
References: Kalhan et
al., Metabolism 37, 152-158, 1988.
Published Glucose Metabolism Studies Analyzed
By Metabolic Solutions
1. Phillips, S.M., H.J. Green, M.A., Tarnopolsky,
and S.M. Grant. Decreased glucose turnover after
short-term training is unaccompanied by changes in
muscle oxidative potential. Am J Physiol. 269(32):E222-E230,
1995.
"This study investigated the hypothesis that
training-induced reduction in exercise blood glucose
utilization can occur independently of increases in
muscle mitochondrial potential."
2. Landau, B.R., Wahren, J., Chandramouli, V., Schumann,
W.C., Ekberg, K., Kalhan, S.C. Use of 2H2O
for Estimating rates of Gluconeogenesis. J. Clin. Invest.
95: 272-178, 1995.
"A method is introduced
for estimating the contribution of gluconeogenesis to
glucose production. 2H2O
is administered orally to achieve 0.5% deuterium enrichment
in body water."
3. Chandramouli, V., Ekber, K., Schumann, W.C., Kalhan,
S.C., Wahren, J., Landau, B.R. Quantifying gluconeogenesis
during fasting. Am. J. Physiol. 273(36):E1209-E1215,
1997.
"The use of 2H2O
in estimating gluconeogenesis' contribution to glucose
production (%GNG) was examined during progressive fasting
in three groups of healthy subjects." |
