Measurement of gluconeogenesis in exercising men  by mass isotopomer distribution analysis

We evaluated the hypothesis that coordinated adjustments in absolute rates of gluconeogenesis (GNGab) and hepatic glycogenolysis (Gly) would maintain euglycemia and match glucose production (GP) to peripheral utilization during rest and exercise. Specifically, we evaluated the extent to which gradations in exercise power output would affect the contribution of GNGab to GP. For these purposes, we employed mass isotopomer distribution analysis (MIDA) and isotope-dilution techniques on eight postabsorptive (PA) endurance-trained men during 90 min of leg cycle ergometry at 45 and 65% peak O2 consumption (V˙o 2 peak; moderate and hard intensities, respectively) and the preceding rest period. GP was constant in resting subjects, whereas the fraction from GNG (fGNG) increased over time during rest (22.3 ± 0.9% at 11.25 h PA vs. 25.6 ± 0.9% at 12.0 h PA, P < 0.05). In the transition from rest to exercise, GP increased in an intensity-dependent manner (rest, 2.0 ± 0.1; 45%, 4.0 ± 0.4; 65%, 5.84 ± 0.64 mg · kg−1 · min−1, P < 0.05), although glucose rate of disappearance exceeded rate of appearance during the last 30 min of exercise at 65%V˙o 2 peak. Compared with rest, increases in GP were sustained by 92 and 135% increments in GNGab during moderate- and hard-intensity exercises, respectively. Correspondingly, Gly (calculated as the difference between GP and MIDA-measured GNGab) increased 100 and 203% over rest during the two exercise intensities. During moderate-intensity exercise, fGNG was the same as at rest; however, during the harder exercise fGNG decreased significantly to account for only 21% of GP. The highest sustained GNGab observed in these trials on PA men was 1.24 ± 0.3 mg · kg−1 · min−1. We conclude that, after an overnight fast, 1) absolute GNG rates increased with intensity of effort despite a reduced fGNG at 65% V˙o 2 peak, 2) during exercise Gly is more responsible than GNGab for maintaining GP, and 3) in 12-h fasted men, neither increased Gly or GNGab nor was their combination able to maintain euglycemia during prolonged hard (65%V˙o 2 peak) exercise.

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Measuring gluconeogenesis with [2-13C]glycerol and mass isotopomer distribution analysis of glucose

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.1995.269.3.e516 ◽

1995 ◽

Vol 269 (3) ◽

pp. E516-E523 ◽

Cited By ~ 12

Author(s):

O. Peroni ◽

V. Large ◽

M. Beylot

Keyword(s):

Glucose Production ◽

Distribution Analysis ◽

Isotopomer Distribution ◽

Mass Isotopomer Distribution Analysis ◽

Total Glucose ◽

Glucose Output ◽

Total Glycerol ◽

Mass Isotopomer

We tested the validity of the use of [2-13C]glycerol and of the mass isotopomer distribution analysis of glucose for measuring gluconeogenesis in vitro and in vivo. When isolated rat livers (starved for 48 h) were infused with labeled glycerol without or with lactate+pyruvate, gluconeogenesis accounted for > 90% of glucose production. When glucose was added to the infusate so that glucose produced by the liver represented only 80 or 45% of total glucose output, this dilution could be calculated from the mass isotopomer distribution of glucose. When postabsorptive and starved rats were infused with [2-13C]glycerol, gluconeogenesis accounted for 54 +/- 2 and 89 +/- 1%, respectively, of glucose production. However, accurate measures could be obtained, particularly in postabsorptive rats, only with high tracer infusion rates (representing > or = 50% of endogenous glycerol production rate). In both groups of rats, these infusion rates resulted in an increase in total glycerol turnover rate and gluconeogenesis from glycerol. In addition, hepatic concentration of glycerol 3-phosphate was increased. In conclusion, [2-13C]glycerol infusion and mass isotopomer distribution analysis of glucose appear to be useful methods for studies of gluconeogenesis in vitro and in vivo; however, accurate measurements in vivo can be obtained only at the expense of some perturbation of the metabolic pathway studied.

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A critical evaluation of mass isotopomer distribution analysis of gluconeogenesis in vivo

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.1999.277.1.e154 ◽

1999 ◽

Vol 277 (1) ◽

pp. E154-E160 ◽

Cited By ~ 10

Author(s):

Stephen F. Previs ◽

Gary W. Cline ◽

Gerald I. Shulman

Keyword(s):

Critical Evaluation ◽

Glucose Production ◽

Distribution Analysis ◽

Isotopomer Distribution ◽

Mass Isotopomer Distribution Analysis ◽

Group I ◽

Total Glucose ◽

Total Glycerol ◽

Mass Isotopomer

There are conflicting reports concerning the reliability of mass isotopomer distribution analysis (MIDA) for estimating the contribution of gluconeogenesis to total glucose production (f) during [13C]glycerol infusion. 1 We have evaluated substrate-induced effects on rate of appearance (Ra) of glycerol and glucose and f during [2-13C]glycerol infusion in vivo. Five groups of mice were fasted for 30 h and then infused with [2-13C]glycerol at variable rates and variable 13C enrichments ( group I: 20 μmol ⋅ kg−1 ⋅ min−1, 99% 13C; group II: 60 μmol ⋅ kg−1 ⋅ min−1, 60% 13C; group III: 60 μmol ⋅ kg−1 ⋅ min−1, 99% 13C; group IV: 120 μmol ⋅ kg−1 ⋅ min−1, 40% 13C; or group V: 120 μmol ⋅ kg−1 ⋅ min−1, 99% 13C). The total glycerol Ra increased from ∼104 to ∼157 and to ∼210 μmol ⋅ kg−1 ⋅ min−1as the infusion of [2-13C]glycerol increased from 20 to 60 and to 120 μmol ⋅ kg− 1 ⋅ min−1, respectively. As the amount of 99% enriched [2-13C]glycerol increased from 20 to 60 and to 120 μmol ⋅ kg−1 ⋅ min−1( groups I, III, and V, respectively), plasma glycerol enrichment increased from ∼21 to ∼42 and to ∼57% and the calculated f increased from ∼27 to ∼56 and to ∼87%, respectively. Similar plasma glycerol enrichments were observed in groups I, II, and IV (i.e., ∼21–24%), yet f increased from ∼27 to ∼57 and to ∼86% in groups II and IV, respectively. Estimates of absolute gluconeogenesis increased from ∼14 to ∼33 and ∼86 μmol ⋅ kg−1 ⋅ min−1as the infusion of [2-13C]glycerol increased from 20 to 60 and 120 μmol ⋅ kg−1 ⋅ min−1. Plausible estimates of f were obtained only under conditions that increased total glycerol Ra∼2-fold ( P < 0.001) and increased glucose Ra ∼1.5-fold ( P < 0.01) above basal. We conclude that in 30-h fasted mice, 1) estimates of f by MIDA with low infusion rates of [2-13C]glycerol yield erroneous results and 2) reasonable estimates of f are obtained at glycerol infusion rates that perturb glycerol and glucose metabolism.

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Calculations for Gluconeogenesis by Mass Isotopomer Distribution Analysis

Journal of Biological Chemistry ◽

10.1016/s0021-9258(17)48643-1 ◽

1995 ◽

Vol 270 (24) ◽

pp. 14464-14466

Author(s):

Richard A. Neesa ◽

Marc K. Hellerstein

Keyword(s):

Distribution Analysis ◽

Isotopomer Distribution ◽

Mass Isotopomer Distribution Analysis ◽

Mass Isotopomer

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Software LS-MIDA for efficient mass isotopomer distribution analysis in metabolic modelling

BMC Bioinformatics ◽

10.1186/1471-2105-14-218 ◽

2013 ◽

Vol 14 (1) ◽

pp. 218 ◽

Cited By ~ 12

Author(s):

Zeeshan Ahmed ◽

Saman Zeeshan ◽

Claudia Huber ◽

Michael Hensel ◽

Dietmar Schomburg ◽

...

Keyword(s):

Distribution Analysis ◽

Metabolic Modelling ◽

Isotopomer Distribution ◽

Mass Isotopomer Distribution Analysis ◽

Mass Isotopomer

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Newly synthesized cholesterol in human bile and plasma: quantitation by mass isotopomer distribution analysis

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.1997.272.2.g367 ◽

1997 ◽

Vol 272 (2) ◽

pp. G367-G373 ◽

Cited By ~ 5

Author(s):

K. Empen ◽

K. Lange ◽

E. F. Stange ◽

J. Scheibner

Keyword(s):

De Novo ◽

Charge Ratio ◽

Gas Chromatography Mass Spectrometry ◽

Distribution Analysis ◽

Biliary Cholesterol ◽

Human Bile ◽

Isotopomer Distribution ◽

Mass Isotopomer Distribution Analysis ◽

Fractional Synthesis ◽

Mass Isotopomer

The purpose of this study was to quantitate the contribution of newly synthesized cholesterol to bile and plasma in humans. Eight healthy volunteers were intravenously infused with 0.125 mmol of [1-(13)C]acetate per kilogram per hour for 15 h. During continuous enteral nutrition, plasma aliquots and samples of duodenal bile were collected hourly. The trimethysilylether of unesterified cholesterol was analyzed by gas chromatography-mass spectrometry for quantitation of the mass fragments M(+0) [mass-to-charge ratio (m/z) 368], M(+1) (m/z 369), M(+2) (m/z 370), M(+3) (m/z 371), and M(+4) (m/z 372). The fractional syntheses of plasma and biliary cholesterol were determined using mass isotopomer distribution analysis. After 6 h of infusion, the 13C enrichment of the acetate pool remained constant at 12%. The fractional synthesis increased continuously during [13C]acetate infusion and reached 4.2% and 5.3% in cholesterol of plasma and bile, respectively. Both were highly correlated, but the fractional synthesis of biliary cholesterol exceeded that of plasma (P < 0.05). It may be concluded that the contribution of de novo cholesterol synthesis to bile exceeds that to plasma but is minor in humans.

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