Quantifying gluconeogenesis during fasting

1997 ◽  
Vol 273 (6) ◽  
pp. E1209-E1215 ◽  
Author(s):  
Visvanathan Chandramouli ◽  
Karin Ekberg ◽  
William C. Schumann ◽  
Satish C. Kalhan ◽  
John Wahren ◽  
...  
Keyword(s):  
Steady State ◽  
Blood Glucose ◽  
Healthy Subjects ◽  
Glucose Production ◽  
Body Water ◽  
Glucose Infusion ◽  
Apparent Change ◽  
State 1

The use of2H2O in estimating gluconeogenesis’ contribution to glucose production (%GNG) was examined during progressive fasting in three groups of healthy subjects. One group ( n = 3) ingested2H2O to a body water enrichment of ≈0.35% 5 h into the fast. %GNG was determined at 2-h intervals from the ratio of the enrichments of the hydrogens at C-5 and C-2 of blood glucose, assayed in hexamethylenetetramine. %GNG increased from 40 ± 8% at 10 h to 93 ± 6% at 42 h. Another group ingested2H2O over 2.25 h, beginning at 11 h ( n = 7) and 19 h ( n = 7) to achieve ≈0.5% water enrichment. Enrichment in plasma water and at C-2 reached steady state ≈1 h after completion of2H2O ingestion. The C-5-to-C-2 ratio reached steady state by the completion of 2H2O ingestion. %GNG was 54 ± 2% at 14 h and 64 ± 2% at 22 h. A 3-h [6,6-2H2]glucose infusion was also begun to estimate glucose production from enrichments at C-6, again in hexamethylenetetramine. Glucose produced by gluconeogenesis was 0.99 ± 0.06 mg ⋅ kg−1 ⋅ min−1at both 14 and 22 h. In a third group ( n = 3) %GNG reached steady state ≈2 h after2H2O ingestion to only ≈0.25% enrichment. In conclusion, %GNG by 2 h after2H2O ingestion and glucose production using [6,6-2H2]glucose infusion, begun together, can be determined from hydrogen enrichments at blood glucose C-2, C-5, and C-6. %GNG increases gradually from the postabsorptive state to 42 h of fasting, without apparent change in the quantity of glucose produced by gluconeogenesis at 14 and 22 h.

Limitations in estimating gluconeogenesis and Cori cycling from mass isotopomer distributions using [U-13C6]glucose

1998 ◽  
Vol 274 (5) ◽  
pp. E954-E961 ◽  
Author(s):  
Bernard R. Landau ◽  
John Wahren ◽  
Karin Ekberg ◽  
Stephen F. Previs ◽  
Dawei Yang ◽  
...  
Keyword(s):  
Amino Acids ◽  
Blood Glucose ◽  
Isotopic Exchange ◽  
Glucose Production ◽  
Normal Subjects ◽  
Glucose Infusion ◽  
Arterial Lactate ◽  
Overnight Fasting ◽  
Mass Isotopomer

Tayek and Katz proposed calculating gluconeogenesis’s contributions to glucose production and Cori cycling from mass isotopomer distributions in blood glucose and lactate during [U-13C6]glucose infusion [Tayek, J. A., and J. Katz. Am. J. Physiol. 272 ( Endocrinol. Metab. 35): E476–E484, 1997]. However, isotopic exchange was not adequately differentiated from dilution, nor was condensation of labeled with unlabeled triose phosphates properly equated. We introduce and apply corrected equations to data from subjects fasted for 12 and 60 h. Impossibly low contributions of gluconeogenesis to glucose production at 60 h are obtained (23–41%). Distributions in overnight-fasted normal subjects calculate to only ∼18%. Cori cycling estimates are ∼10–15% after overnight fasting and 20% after 60 h of fasting. There are several possible reasons for the underestimates. The contribution of gluconeogenesis is underestimated because glucose production from glycerol and amino acids not metabolized via pyruvate is ascribed to glycogenolysis. Labeled oxaloacetate and α-ketoglutarate can exchange during equilibrium with circulating unlabeled aspartate, glutamate, and glutamine. Also, the assumption that isotopomer distributions in arterial lactate and hepatic pyruvate are the same may not be fulfilled.

Effects of physiological hyperinsulinemia on the intracellular metabolic partition of plasma glucose

1993 ◽  
Vol 265 (6) ◽  
pp. E943-E953 ◽  
Author(s):  
R. C. Bonadonna ◽  
S. del Prato ◽  
E. Bonora ◽  
G. Gulli ◽  
A. Solini ◽  
...  
Keyword(s):  
Plasma Glucose ◽  
Healthy Subjects ◽  
Glucose Oxidation ◽  
Hepatic Glucose Production ◽  
Glycogen Synthesis ◽  
Glucose Production ◽  
Glucose Infusion ◽  
Glucose Disposal ◽  
Hepatic Glucose ◽  
Glucose Recycling

Methodology for assessing the glycolytic and oxidative fluxes from plasma glucose, by measuring 3H2O and 14CO2 rates of production during [3-3H]- and [U-14C]glucose infusion, was tested in healthy subjects. In study 1, during staircase 3H2O infusion in six subjects, calculated rates of 3H2O appearance agreed closely with 3H2O infusion rates. In study 2, when [2-3H]glucose and NaH14CO3 were infused in four subjects in the basal state and during a 4-h euglycemic insulin (approximately 70 microU/ml) clamp, accurate estimates of the rates of [2-3H]glucose detritiation were obtained (94-97% of the expected values), and the recovery factor of NaH14CO3 did not change during hyperinsulinemia. In study 3, 11 subjects underwent a 4-h euglycemic insulin (approximately 70 microU/ml) clamp with [3-3H]- and [U-14C]glucose infusion and measurement of gaseous exchanges by indirect calorimetry to estimate the rates of total glycolysis, glycogen synthesis, glucose oxidation, nonoxidative glycolysis, hepatic glucose production, glucose recycling, and glucose conversion to fat. Hyperinsulinemia stimulated glycogen synthesis above baseline more than glycolysis [increment of 4.78 +/- 0.37 vs. 2.0 +/- 0.17 mg.min-1 x kg-1 of lean body mass (LBM), respectively, P < 0.01] and incompletely suppressed (approximately 87%) hepatic glucose production. The major component of nonoxidative glycolysis shifted from glucose recycling in the postabsorptive state (approximately 57% of nonoxidative glycolysis) to glucose conversion to fat during hyperinsulinemia (approximately 59% of nonoxidative glycolysis). Lipid oxidation during the insulin clamp was negatively correlated with both isotopic glucose oxidation (r = -0.822, P < 0.002) and glycolysis (r = -0.582, P < 0.07). In conclusion, in healthy subjects, glycogen synthesis plays a greater role than glycolysis and glucose oxidation in determining insulin-mediated glucose disposal. Part of insulin-mediated increase in glycolysis/oxidation might be secondary to the relief of the competition between fat and glucose for oxidation.

scholarly journals Portal glucose infusion-glucose clamp measures hepatic influence on postprandial systemic glucose appearance as well as whole body glucose disposal

2010 ◽  
Vol 298 (2) ◽  
pp. E346-E353 ◽  
Author(s):  
Dan Zheng ◽  
Viorica Ionut ◽  
Vahe Mooradian ◽  
Darko Stefanovski ◽  
Richard N. Bergman
Keyword(s):  
Steady State ◽  
Portal Vein ◽  
Glucose Production ◽  
Glucose Clamp ◽  
Glucose Infusion ◽  
Whole Body ◽  
Glucose Disposal ◽  
Exogenous Glucose ◽  
Hepatic Glucose ◽  
Glucose Supply

The full impact of the liver, through both glucose production and uptake, on systemic glucose appearance cannot be readily studied in a classical glucose clamp because hepatic glucose metabolism is regulated not only by portal insulin and glucose levels but also portal glucose delivery (the portal signal). In the present study, we modified the classical glucose clamp by giving exogenous glucose through portal vein, the “portal glucose infusion (PoG)-glucose clamp”, to determine the net hepatic effect on postprandial systemic glucose supply along with the measurement of whole body glucose disposal. By comparing systemic rate of glucose appearance (Ra) with portal glucose infusion rate (PoGinf), we quantified “net hepatic glucose addition (NHGA)” in the place of endogenous glucose production determined in a regular clamp. When PoG-glucose clamps ( n = 6) were performed in dogs at basal insulinemia and hyperglycemia (∼150 mg/dl, portal and systemic), we measured consistently higher Ra than PoGinf (4.2 ± 0.6 vs. 2.9 ± 0.6 mg·kg−1·min−1 at steady state, P < 0.001) and thus positive NHGA at 1.3 ± 0.1 mg·kg−1·min−1, identifying net hepatic addition of glucose to portal exogenous glucose. In contrast, when PoG-glucose clamps ( n = 6) were performed at hyperinsulinemia (∼250 pmol/l) and systemic euglycemia (portal hyperglycemia due to portal glucose infusion), we measured consistently lower Ra than PoGinf (13.1 ± 2.4 vs. 14.3 ± 2.4 mg·kg−1·min−1, P < 0.001), and therefore negative NHGA at −1.1 ± 0.1 mg·kg−1·min−1, identifying a switch of the liver from net production to net uptake of portal exogenous glucose. Steady-state whole body glucose disposal was 4.1 ± 0.5 and 13.0 ± 2.4 mg·kg−1·min−1, respectively, determined as in a classical glucose clamp. We conclude that the PoG-glucose clamp, simulating postprandial glucose entry and metabolism, enables simultaneous assessment of the net hepatic effect on postprandial systemic glucose supply as well as whole body glucose disposal in various animal models (rodents, dogs, and pigs) with established portal vein catheterization.

Measuring gluconeogenesis using a low dose of2H2O: advantage of isotope fractionation during gas chromatography

2003 ◽  
Vol 284 (5) ◽  
pp. E1043-E1048 ◽  
Author(s):  
Jill Katanik ◽  
Brendan J. McCabe ◽  
Daniel Z. Brunengraber ◽  
Visvanathan Chandramouli ◽  
Fumie J. Nishiyama ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Gas Chromatography ◽  
Blood Glucose ◽  
Isotope Fractionation ◽  
Low Dose ◽  
Glucose Production ◽  
Body Water ◽  
Gas Chromatography Mass Spectrometry ◽  
Chromatographic Retention ◽  
The Difference

The contribution of gluconeogenesis to glucose production can be measured by enriching body water with2H2O to ∼0.5% 2H and determining the ratio of 2H that is bound to carbon-5 vs. carbon-2 of blood glucose. This labeling ratio can be measured using gas chromatography-mass spectrometry after the corresponding glucose carbons are converted to formaldehyde and then to hexamethylenetetramine (HMT). We present a technique for integrating ion chromatograms that allows one to use only 0.05% 2H in body water (i.e., 10 times less than the current dose). This technique takes advantage of the difference in gas chromatographic retention times of naturally labeled HMT and [2H]HMT. We discuss the advantage(s) of using a low dose of 2H2O to quantify the contribution of gluconeogenesis.

Pulsatile hyperglucagonemia fails to increase hepatic glucose production in normal man

1987 ◽  
Vol 252 (1) ◽  
pp. E1-E7 ◽  
Author(s):  
G. Paolisso ◽  
A. J. Scheen ◽  
A. S. Luyckx ◽  
P. J. Lefebvre
Keyword(s):  
Blood Glucose ◽  
Hepatic Glucose Production ◽  
Glucose Production ◽  
Glucose Infusion ◽  
Metabolic Effects ◽  
Glucose Turnover ◽  
Continuous Administration ◽  
Hepatic Glucose ◽  
Normal Man

To study the metabolic effects of pulsatile glucagon administration, six male volunteers were submitted to a 260-min glucose-controlled glucose intravenous infusion using the Biostator. The endogenous secretion of the pancreatic hormones was inhibited by somatostatin (100 micrograms X h-1), basal insulin secretion was replaced by a continuous insulin infusion (0.2 mU X kg-1 X min-1), and glucagon was infused intravenously in two conditions at random: either continuously (125 ng X min-1) or intermittently (812.5 ng X min-1, with a switching on/off length of 2/11 min). Blood glucose levels and glucose infusion rate were monitored continuously by the Biostator, and classical methodology using a D-[3-3H]glucose infusion allowed us to study glucose turnover. While basal plasma glucagon levels were similar in both conditions (122 +/- 31 vs. 115 +/- 18 pg X ml-1), they plateaued at 189 +/- 38 pg X ml-1 during continuous infusion and varied between 95 and 501 pg X ml-1 during pulsatile infusion. When compared with continuous administration, pulsatile glucagon infusion initially induced a similar increase in endogenous (hepatic) glucose production and blood glucose, did not prevent the so-called “evanescent” effect of glucagon on blood glucose, and after 3 h tended to reduce rather than increase hepatic glucose production. In conclusion, in vivo pulsatile hyperglucagonemia in normal man fails to increase hepatic glucose production.

Effects of cold exposure and time relative to feeding on glucose metabolism of sheep using a glucose clamp approach

2003 ◽  
Vol 140 (3) ◽  
pp. 335-341 ◽  
Author(s):  
A. TAKEBAYASHI ◽  
H. SANO ◽  
T. FUJITA ◽  
K. AMBO
Keyword(s):  
Blood Glucose ◽  
Glucose Metabolism ◽  
Cold Exposure ◽  
Glucose Production ◽  
Endogenous Glucose Production ◽  
Glucose Clamp ◽  
Glucose Infusion ◽  
Isotope Dilution Method ◽  
Glucose Turnover ◽  
Dilution Method

An experiment combining a hyperinsulinaemic euglycaemic clamp approach and an isotope dilution method determined the effects of cold exposure and time relative to feeding on blood glucose metabolism in four sheep. The sheep, fed 20 g/kg body-weight (BW) of lucerne hay cubes and 5 g/kg BW of maize-based concentrates once daily, were exposed in turn to a thermoneutral environment (20 °C) and a cold environment (0 °C) for 20 days. The combined experiments were performed at four different times relative to feeding, i.e. 3 to 2 h, 2 to 1 h and 1 to 0 h before, and 1 to 2 h after the initiation of feeding for the basal periods, and 1 to 0 h before, and 0 to 1 h, 1 to 2 h and 3 to 4 h after the initiation of feeding for the glucose clamp periods in both environments. [U-13C]Glucose was continuously infused for 6 h after a priming injection. Insulin was continuously infused at 6·0 mU/kg BW per min for 2 h, which corresponded to the last 2 h of the [U-13C]glucose infusion. Blood glucose concentrations were maintained euglycaemic during the insulin infusion by concomitant variable glucose infusion. Blood glucose turnover rate (GTR) during the basal period was enhanced by cold exposure (P=0·01) and feeding (P=0·04). Blood GTR increased (P<0·01) with the glucose clamp. During the glucose clamp, blood GTR and glucose infusion rate (GIR) were greater (P=0·003 and P=0·001, respectively) during cold exposure than in the thermoneutral environment. Time relative to feeding influenced (P=0·003) the GIR, whereas changes in blood GTR and endogenous glucose production rate were not significant. No significant cold×feeding interaction was observed in these variables. It was suggested that, in sheep, glucose metabolism was enhanced by cold exposure and the glucose clamp. It was probable that blood glucose metabolism during the glucose clamp was influenced by cold exposure and feeding, but the combined effect of cold exposure and feeding was not significant.

Effects of somatostatin and glucose infusion on glucose kinetics in fetal sheep

1988 ◽  
Vol 255 (1) ◽  
pp. E87-E93
Author(s):  
C. A. Bloch ◽  
R. K. Menon ◽  
M. A. Sperling
Keyword(s):  
Steady State ◽  
Blood Glucose ◽  
Infusion Rate ◽  
Plasma Insulin ◽  
Glucose Infusion ◽  
Plasma Glucagon ◽  
Glucose Kinetics ◽  
Fetal Sheep ◽  
Sequence Protocol

We examined the contribution of glucose, independently of insulin, on fetal glucose kinetics in the sheep by infusing somatostatin (SRIF), followed by SRIF plus glucose (protocol A) or reversing the initial infusion sequence (protocol B). In protocol A (n = 8), infusion of SRIF at 200 micrograms/h decreased plasma insulin (IRI) and blood glucose (G) by 2.8 +/- 1.0 microU/ml and 1.34 +/- 0.2 mg/dl from their respective basal concentrations of 6.8 +/- 1.4 microU/ml and 16.47 +/- 0.91 mg/dl (P less than 0.05; P less than 0.005). There were no significant changes in plasma glucagon (IRG) or the rates of umbilical G uptake or of G utilization, but G turnover decreased by 1.77 +/- 0.34 mg.kg-1.min-1 (P less than 0.005). Addition of G at a rate of 5.6 +/- 0.8 mg.kg-1.min-1 had no effect on IRI and IRG. Total G uptake (G infusion rate plus umbilical G uptake) increased from 6.37 +/- 0.77 to 10.25 +/- 1.0 mg.kg-1.min-1 (P less than 0.01), despite suppression of umbilical G uptake by 33%. Fetal G reached a new steady state of 23.08 +/- 1.37 mg/dl, and G turnover increased by 4.81 +/- 0.96 mg.kg-1.min-1 from its SRIF-induced nadir (P less than 0.005). Since G concentration was maintained at steady state, the rate of G utilization was equivalent to the rate of total G uptake, an increase of 60% from basal despite suppressed IRI.(ABSTRACT TRUNCATED AT 250 WORDS)

Dexamethasone increases glucose cycling, but not glucose production, in healthy subjects

1990 ◽  
Vol 259 (5) ◽  
pp. E626-E632 ◽  
Author(s):  
A. Wajngot ◽  
A. Khan ◽  
A. Giacca ◽  
M. Vranic ◽  
S. Efendic
Keyword(s):  
Healthy Subjects ◽  
Glucose Production ◽  
Glucose Infusion ◽  
Metabolic Clearance ◽  
Hepatic Glucose Metabolism ◽  
Oral Dexamethasone ◽  
Hepatic Glucose ◽  
Early Effects ◽  
Total Glucose ◽  
Glucose Output

We established that measurement of glucose fluxes through glucose-6-phosphatase (G-6-Pase; hepatic total glucose output, HTGO), glucose cycling (GC), and glucose production (HGP), reveals early diabetogenic changes in liver metabolism. To elucidate the mechanism of the diabetogenic effect of glucocorticoids, we treated eight healthy subjects with oral dexamethasone (DEX; 15 mg over 48 h) and measured HTGO with [2-3H]glucose and HGP with [6-3H]glucose postabsorptively and during a 2-h glucose infusion (11.1 mumol.kg-1.min-1). [2-3H]- minus [6-3H]glucose equals GC. DEX significantly increased plasma glucose, insulin, C peptide, and HTGO, while HGP was unchanged. In controls and DEX, glucose infusion suppressed HTGO (82 vs. 78%) and HGP (87 vs. 91%). DEX increased GC postabsorptively (three-fold) P less than 0.005 and during glucose infusion (P less than 0.05) but decreased metabolic clearance and glucose uptake (Rd), which eventually normalized, however. Because DEX increased HTGO (G-6-Pase) and not HGP (glycogenolysis + gluconeogenesis), we assume that DEX increases HTGO and GC in humans by activating G-6-Pase directly, rather than by expanding the glucose 6-phosphate pool. Hyperglycemia caused by peripheral effects of DEX can also contribute to an increase in GC by activating glucokinase. Therefore, measurement of glucose fluxes through G-6-Pase and GC revealed significant early effects of DEX on hepatic glucose metabolism, which are not yet reflected in HGP.

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