Calculation of the rate of gluconeogenesis from the incorporation of 14C atoms from labelled bicarbonate or acetate

1982 ◽  
Vol 60 (12) ◽  
pp. 1603-1609 ◽  
Author(s):  
G. Hetenyi Jr. ◽  
B. Lussier ◽  
C. Ferrarotto ◽  
J. Radziuk
Keyword(s):  
Plasma Glucose ◽  
Specific Activity ◽  
Large Fraction ◽  
Glucose Production ◽  
Plasma Urea ◽  
Extrahepatic Tissues ◽  
Glucose Formation ◽  
Metabolic Exchange ◽  
Heavy Labelling

The rate of gluconeogenesis in vivo may be estimated by the incorporation of 14C atoms from a labelled precursor into plasma glucose or by introducing 14C atoms into the pathway of gluconeogenesis at known stages by metabolites which in themselves do not contribute to the net synthesis of glucose (e.g., bicarbonate or acetate). The purpose of the investigation was to examine some of the assumptions involved in the calculation of gluconeogenic flux by the second approach. [2- 14C]acetate or NaH 14CO3 was infused to dogs, and the specific activity (SA) of glucose, bicarbonate CO2, urea, and lactate in the plasma was followed. The incorporation of 14C atoms from [2- 14C]acetate into glucose allows the calculation of the degree of underestimation of glucose formation due to "metabolic exchange" in the hepatic oxaloacetate pool. The possible error introduced into this calculation by the incorporation of 14C atoms from 14CO2 (a product of acetate oxidation) was found to be negligible, but the heavy labelling of plasma lactate may possibly affect the estimate of metabolic exchange. It is proposed that in the calculation of the rate of gluconeogenesis from infused NaHCO3 the SA of hepatocellular and not of plasma bicarbonate CO2 should be related to that of plasma glucose. This latter is expected to equal the SA of plasma urea, since the sole precursor of its C atom is hepatocellular CO2. The rate of gluconeogenesis estimated from the SA(glucose)/SA(urea) ratio and a previously estimated correction factor for metabolic exchange was 51% of the glucose production in the postabsorptive state. The nearly identical SA(urea)/SA(CO2) ratios, irrespective of the tracer infused, indicated that plasma CO2 is a major precursor of urea C and that a large fraction of injected acetate is oxidized by extrahepatic tissues.

Effects of intraruminal infusions of urea, sucrose or urea plus sucrose on plasma urea and glucose kinetics in sheep fed chopped lucerne hay

1993 ◽  
Vol 121 (1) ◽  
pp. 125-130 ◽  
Author(s):  
Y. Obara ◽  
D. W. Dellow
Keyword(s):  
Plasma Glucose ◽  
Rumen Fluid ◽  
Glucose Production ◽  
Ammonia Concentration ◽  
Irreversible Loss ◽  
Glucose Kinetics ◽  
Plasma Urea ◽  
Urea Excretion ◽  
Urea Kinetics ◽  
Plasma Urea Concentration

SUMMARYThe effect of rumen fermentation on the relationship between urea and glucose kinetics was examined in sheep fed chopped lucerne hay with intraruminal infusions of water, urea, sucrose, or urea plus sucrose at Palmerston North, New Zealand in 1986. Sheep were fed hourly and infused intraruminally with water (1200 m1/day), or a similar volume containing either urea alone (13·7g/day), sucrose alone (178·2 g/day) or urea (14·6 g/day) plus sucrose (175·0 g/day). The added sucrose resulted in a lower rumen ammonia concentration (P< 0·05), lower plasma urea concentration (P< 0·05) and reduced urinary urea excretion (P< 0·05). Urea recycled to the gut tended to increase with the sucrose, urea or sucrose plus urea treatments compared with the water treatment. The fermentation of sucrose in the rumen resulted in decreases in ruminal pH (P< 0·05) and in the ratio of acetate to propionate (A:P) (P< 0·05). The infusion of sucrose also increased the concentration of propionate in rumen fluid (P< 0·05), tended to increase the plasma glucose level and increased plasma glucose irreversible loss (P< 0·05). The infusion of urea resulted in an increase in the plasma urea level (P< 0·05), urea pool size (P< 0·05) and urea irreversible loss (P< 0·01). However, urea infusion did not affect glucose metabolism or volatile fatty acid (VFA) fermentation. The effects of sucrose infusion on glucose and urea kinetics were broadly similar when given alone or with urea, apart from changes in the urea degradation rate. It was concluded that the additional fermentative activity resulting from sucrose increased propionate production which, in turn, was available for glucose production, thus ‘sparing’ amino acids for tissue protein utilization and reducing urea excretion.

Model of the kinetics of ketone bodies in humans

1982 ◽  
Vol 243 (1) ◽  
pp. R7-R17 ◽  
Author(s):  
C. Cobelli ◽  
R. Nosadini ◽  
G. Toffolo ◽  
A. McCulloch ◽  
A. Avogaro ◽  
...  
Keyword(s):  
Ketone Body ◽  
Specific Activity ◽  
Ketone Bodies ◽  
Mathematical Representation ◽  
Parameter Estimates ◽  
Extrahepatic Tissues ◽  
Body Compartments ◽  
Body Production ◽  
Kinetics Of

The kinetics of ketone bodies was studied in normal humans by giving a combined bolus intravenous injection of labeled acetoacetate ([14C]AcAc) and D(--)-beta-hydroxybutyrate (beta-[14C]-OHB) to seven subjects after an overnight fast, on two different occasions, and by collecting frequent blood samples for 100 min. Kinetic data were analyzed with both noncompartmental and compartmental modeling techniques. A four-compartment model, representing AcAc and beta-OHB in blood and two equilibrating ketone body compartments, inside the liver and extrahepatic tissues, was chosen as the most reliable mathematical representation; it is physiologically plausible and was able to accurately fit the data. The model permitted evaluation of the in vivo rate of ketone body production in the liver, the individual plasma clearance rates of AcAc and beta-OHB, their initial volumes of distribution, and the transfer rate parameters among the four ketone body compartments. Moreover, the model provided estimates of the components of the rates of appearance of AcAc and beta-OHB in plasma due to newly synthesized ketone body from acetyl-CoA in the liver, and to interconversion and recycling in the liver and extrahepatic tissues. The model also was used to evaluate other methodologies currently employed in the analysis of ketone body turnover data: the conventional approach based on use of the combined specific activity of AcAc and beta-OHB required assumptions not satisfied in vivo, leading to substantial errors in key parameter estimates.

EFFECTS OF INSULIN ON RATES OF GLUCOSE TRANSFER IN THE DEPANCREATIZED DOG

1955 ◽  
Vol 33 (6) ◽  
pp. 926-939 ◽  
Author(s):  
Margaret J. Henderson ◽  
Gerald A. Wrenshall ◽  
Paul Odense
Keyword(s):  
Plasma Glucose ◽  
Dynamic Equilibrium ◽  
Specific Activity ◽  
The State ◽  
Time Intervals ◽  
Lower Blood Glucose ◽  
In Vivo Experiments ◽  
Lower Blood ◽  
Before And After

An attempt to answer the question as to whether insulin acts to lower blood glucose by increasing utilization, or by decreasing production, or by both, has been made using a new experimental approach. A trace dose of radioactive glucose was injected into each of six postabsorptive depancreatized dogs which had been deprived of exogenous insulin for 66 hr. Blood samples were collected before and after the intravenous injection of insulin, and plasma glucose concentration and specific activity were measured. From these data the simultaneous rates of appearance and disappearance of plasma glucose were calculated for a sequence of time intervals, both before and after insulin, by a method which did not assume dynamic equilibrium. Previous in vivo experiments using radioactive tracers to measure rates of production and utilization of glucose have been made in animals which were in steady states, either with or without insulin, and the effects of insulin were ascertained by comparison of the state with insulin and the state without insulin. The method described in this paper has made it possible to follow the effects of insulin while it is acting in one and the same animal. Insulin was found to cause an abrupt and marked increase in the rate of disappearance of glucose, and this increased rate became less with time, reaching the preinsulin level in about 90 min. Insulin caused a slower and much smaller decrease in the rate of appearance, but the decrease became greater with time during the three hour period of observation. Thus, it appeared that insulin acted in vivo both to increase the utilization of glucose and to decrease its production, but the effects differed in magnitude and in speed of response.

scholarly journals Mass spectrometry-based microassay of 2H and 13C plasma glucose labeling to quantify liver metabolic fluxes in vivo

2015 ◽  
Vol 309 (2) ◽  
pp. E191-E203 ◽  
Author(s):  
Clinton M. Hasenour ◽  
Martha L. Wall ◽  
D. Emerson Ridley ◽  
Curtis C. Hughey ◽  
Freyja D. James ◽  
...  
Keyword(s):  
Steady State ◽  
Plasma Glucose ◽  
Ad Hoc ◽  
Citrate Synthase ◽  
Physiological Stress ◽  
Glucose Production ◽  
Endogenous Glucose Production ◽  
Hepatic Glucose

Mouse models designed to examine hepatic metabolism are critical to diabetes and obesity research. Thus, a microscale method to quantitatively assess hepatic glucose and intermediary metabolism in conscious, unrestrained mice was developed. [13C3]propionate, [2H2]water, and [6,6-2H2]glucose isotopes were delivered intravenously in short- (9 h) and long-term-fasted (19 h) C57BL/6J mice. GC-MS and mass isotopomer distribution (MID) analysis were performed on three 40-μl arterial plasma glucose samples obtained during the euglycemic isotopic steady state. Model-based regression of hepatic glucose and citric acid cycle (CAC)-related fluxes was performed using a comprehensive isotopomer model to track carbon and hydrogen atom transitions through the network and thereby simulate the MIDs of measured fragment ions. Glucose-6-phosphate production from glycogen diminished, and endogenous glucose production was exclusively gluconeogenic with prolonged fasting. Gluconeogenic flux from phospho enolpyruvate (PEP) remained stable, whereas that from glycerol modestly increased from short- to long-term fasting. CAC flux [i.e., citrate synthase ( V CS)] was reduced with long-term fasting. Interestingly, anaplerosis and cataplerosis increased with fast duration; accordingly, pyruvate carboxylation and the conversion of oxaloacetate to PEP were severalfold higher than V CS in long-term fasted mice. This method utilizes state-of-the-art in vivo methodology and comprehensive isotopomer modeling to quantify hepatic glucose and intermediary fluxes during physiological stress in mice. The small plasma requirements permit serial sampling without stress and the affirmation of steady-state glucose kinetics. Furthermore, the approach can accommodate a broad range of modeling assumptions, isotope tracers, and measurement inputs without the need to introduce ad hoc mathematical approximations.

Pseudoketogenesis in hepatectomized dogs

1990 ◽  
Vol 258 (3) ◽  
pp. E519-E528 ◽  
Author(s):  
C. Des Rosiers ◽  
J. A. Montgomery ◽  
M. Garneau ◽  
F. David ◽  
O. A. Mamer ◽  
...  
Keyword(s):  
Bolus Injection ◽  
Specific Activity ◽  
Ketone Bodies ◽  
Gas Chromatography Mass Spectrometry ◽  
Selected Ion Monitoring ◽  
Coa Transferase ◽  
Net Uptake ◽  
Extrahepatic Tissues ◽  
Molar Percent

Overestimation of ketone body turnover in vivo, measured by tracer kinetics, could occur if specific activity or molar percent enrichment is diluted in extrahepatic tissues by label exchange via reversal of 3-oxoacid-CoA transferase, a process we call pseudoketogenesis. To test this hypothesis, euglycemic hepatectomized dogs were injected with a bolus of acetoacetate (0.8 mmol/kg), 32% enriched in [3,4-13C2]acetoacetate. Concentrations and labeling patterns of blood acetoacetate and R-3-hydroxybutyrate were measured by selected ion-monitoring gas chromatography-mass spectrometry. During the 60 min after bolus injection of [3,4-13C2]acetoacetate, the molar percent enrichment of blood [3,4-13C2]acetoacetate decreased to 73 +/- 3% (n = 5) in controls and to 11.5 +/- 0.8% (n = 3) during infusion of dichloroacetate, an activator of pyruvate dehydrogenase. The enrichment of R-3-hydroxy-[3,4-13C2]butyrate followed closely that of [3,4-13C2]acetoacetate. These dilutions occurred despite a net uptake of ketone bodies. Concomitantly, 10.6 +/- 2.2 (n = 5) and 6.0 +/- 2.9% (n = 3) of [13C]acetoacetate molecules were labeled on all four carbons in control and dichloroacetate-treated dogs, respectively. This uniformly labeled acetoacetate arises from partial equilibration between [3,4-13C2]acetoacetate and [1,2-13C2]acetyl-CoA via the reactions catalyzed by 3-oxoacid-CoA transferase and acetoacetyl-CoA thiolase. Our data demonstrate the reversibility of the 3-oxoacid-CoA transferase in intact extrahepatic tissues and support the concept of pseudoketogenesis. This phenomenon has been quantitated by kinetic analysis of the data.

Correction factor for the estimation of plasma glucose synthesis from the transfer of 14C-atoms from labelled substrate in vivo: A preliminary report

1979 ◽  
Vol 57 (7) ◽  
pp. 767-770 ◽  
Author(s):  
G. Hetenyi Jr.
Keyword(s):  
Correction Factor ◽  
Plasma Glucose ◽  
Preliminary Report ◽  
Glucose Synthesis ◽  
Diabetic Dogs ◽  
Metabolic Exchange

Based on a previously designed method for the estimation of the contribution of C-atoms by acetylcoenzyme A to the hepatic oxaloacetate pool, the loss of 14C-atoms on their way from a precursor to plasma glucose due to 'metabolic exchange' was estimated in normal and diabetic dogs and in normal rats. Due to this loss of 14C-atoms, the rates of gluconeogenesis when calculated from the transfer of 14C-atoms from precursors (other than glycerol) are underestimated by a factor of 2.2 ± 0.07 in normal, 1.8 ± 0.05 in diabetic dogs, and by 1.55 ± 0.04 in normal rats.

scholarly journals The Action of Pitressin on Solute Permeability of the Rabbit Nephron in Vivo

1966 ◽  
Vol 50 (1) ◽  
pp. 1-8 ◽  
Author(s):  
E. C. Foulkes
Keyword(s):  
Specific Activity ◽  
Specific Effect ◽  
Renal Medulla ◽  
Urine Flow ◽  
Intraarterial Infusion ◽  
Plasma Urea ◽  
Solute Permeability ◽  
Isotopic Equilibration ◽  
Constant Specific Activity

The isotopic equilibration of urea, thiourea, and inulin between urine and plasma was determined in rabbits in the presence or absence of antidiuretic hormone (ADH). Animals were anesthetized with ethanol and permitted to reach steady state after completion of surgery. Tracer was then administered by intraarterial infusion in such a manner that a high constant specific activity in plasma was rapidly attained. Urine flow was kept independent of ADH by addition of mannitol. Urea/creatinine clearance ratios and the accumulation of urea in renal medulla and papilla also remained unaffected by ADH. Under these conditions, thiourea and inulin at all times approached equilibrium, at similar rates. In the absence of ADH, urea also equilibrated at a rate similar to that of inulin. The addition of ADH, however, significantly prolonged the delay before urinary urea reached the high constant specific activity of plasma urea. These observations are interpreted in terms of a specific effect of the hormone on the solute permeability of the nephron.

scholarly journals Effects of Somatostatin and Glucagon on the Utilization of [2_14C] Propionate in Glucose Production in Vivo in Sheep

1980 ◽  
Vol 33 (4) ◽  
pp. 457 ◽  
Author(s):  
Ronald P Brockman ◽  
Cindy Greer
Keyword(s):  
Continuous Infusion ◽  
Plasma Glucose ◽  
Control Period ◽  
Specific Radioactivity ◽  
Glucose Production ◽  
Irreversible Loss ◽  
Selective Effect ◽  
Glycogenolytic Effect ◽  
Glucose Synthesis

This study examined the effects of hypoglucagonaemia and hyperglucagonaemia on the incorporation of 14C from [2-14C]propionate into plasma glucose of sheep in vivo. The sheep were adult ewes fed a maintenance diet of lucerne pellets delivered in equal aliquots hourly. The irreversible loss of glucose was determined by the continuous infusion of [6-3H]glucose. During the control period (the hour immediately preceding infusion of hormones) 63 �2 % of the propionate was converted to glucose, accounting for 30�2 % of glucose production. Glucagon deficiency, induced by infusion of somatostatin (100 J1g/h), did not affect gluconeogenesis and the irreversible loss of glucose significantly. However, glucagon infusion at 11 �5 �O� 6 J1g/h significantly increased the irreversible loss of glucose, with the greatest increase occurring in the first 15 min of infusion. The 14C specific radioactivity of glucose and the fraction of glucose derived from propionate decreased significantly during glucagon infusion. The data are consistent with glucagon having a marked glycogenolytic effect initially, but little or no selective effect in promoting the utilization of propionate for glucose synthesis in vivo in sheep.

EFFECTS OF INSULIN ON RATES OF GLUCOSE TRANSFER IN THE DEPANCREATIZED DOG

1955 ◽  
Vol 33 (1) ◽  
pp. 926-939 ◽  
Author(s):  
Margaret J. Henderson ◽  
Gerald A. Wrenshall ◽  
Paul Odense
Keyword(s):  
Plasma Glucose ◽  
Dynamic Equilibrium ◽  
Specific Activity ◽  
The State ◽  
Time Intervals ◽  
Lower Blood Glucose ◽  
In Vivo Experiments ◽  
Lower Blood ◽  
Before And After

An attempt to answer the question as to whether insulin acts to lower blood glucose by increasing utilization, or by decreasing production, or by both, has been made using a new experimental approach. A trace dose of radioactive glucose was injected into each of six postabsorptive depancreatized dogs which had been deprived of exogenous insulin for 66 hr. Blood samples were collected before and after the intravenous injection of insulin, and plasma glucose concentration and specific activity were measured. From these data the simultaneous rates of appearance and disappearance of plasma glucose were calculated for a sequence of time intervals, both before and after insulin, by a method which did not assume dynamic equilibrium. Previous in vivo experiments using radioactive tracers to measure rates of production and utilization of glucose have been made in animals which were in steady states, either with or without insulin, and the effects of insulin were ascertained by comparison of the state with insulin and the state without insulin. The method described in this paper has made it possible to follow the effects of insulin while it is acting in one and the same animal. Insulin was found to cause an abrupt and marked increase in the rate of disappearance of glucose, and this increased rate became less with time, reaching the preinsulin level in about 90 min. Insulin caused a slower and much smaller decrease in the rate of appearance, but the decrease became greater with time during the three hour period of observation. Thus, it appeared that insulin acted in vivo both to increase the utilization of glucose and to decrease its production, but the effects differed in magnitude and in speed of response.

The reliability of rates of glucose appearance in vivo calculated from single tracer injections

1979 ◽  
Vol 57 (11) ◽  
pp. 1267-1274 ◽  
Author(s):  
John R. Allsop ◽  
Robert R. Wolfe ◽  
Joseph J. DiStephano III ◽  
John F. Burke
Keyword(s):  
Plasma Glucose ◽  
Infusion Rate ◽  
Specific Radioactivity ◽  
Glucose Production ◽  
Endogenous Glucose Production ◽  
Constant Infusion ◽  
Glucose Turnover ◽  
Time Curve ◽  
The Mean

The rate of appearance of unlabelled glucose was calculated from changes in plasma glucose specific radioactivity after a single intravenous injection of labelled glucose and compared with the actual constant infusion rate of unlabelled glucose into an anaesthetized dog with all sources of endogenous glucose production surgically removed. The mean steady-state rate of appearance of unlabelled glucose calculated from the area under the specific radioactivity versus time curve was 7% higher than the actual infusion rate (n = 4), but the difference was not statistically significant. The variability in the rate calculated in this manner was, however, greater than the variability we have reported with rates determined from a primed constant infusion of tracer. Using 15- to 60- or 60- to 120-min specific radioactivity data the mean rate of appearance of glucose, calculated on the assumption of a one-pool model for glucose turnover in vivo, was approximately 60% higher than the actual infusion rate. The results also indicate that it is possible to construct multi-pool models, but it is difficult to equate specific physiological events with the individual terms of the multi-exponential equation which describes the changes in plasma glucose specific radioactivity.

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