Constant specific activity input allows reconstruction of endogenous glucose concentration in non-steady state

1990 ◽  
Vol 258 (6) ◽  
pp. E1037-E1040 ◽  
Author(s):  
C. Cobelli ◽  
G. Toffolo
Keyword(s):  
Steady State ◽  
Glucose Concentration ◽  
Specific Activity ◽  
Radioactive Tracer ◽  
In Vivo Studies ◽  
Constant Infusion ◽  
Glucose Turnover ◽  
Glucose System ◽  
Constant Specific Activity

In vivo studies on the glucose system often require its perturbation by an exogenous input of glucose, whereas glucose turnover is assessed by infusing a glucose tracer. The constant infusion represents the usual format of tracer administration, but it has no clear advantage other than simplicity. Here we propose a different tracer infusion format. It consists of infusing the tracer in parallel with unlabeled glucose so as to maintain a constant specific activity in the infusate. This protocol does not increase experimental complexity and provides new information on the glucose system in non-steady state by allowing reconstruction of the endogenous component of glucose concentration. This reconstruction only requires very general assumptions, such as tracer-tracee indistinguishability and mass conservation; in particular it is independent of the glucose model structure, i.e., number of compartments and their interconnections. A proof of the result is given for a general nonlinear model of the glucose system. The constant specific activity input is also advantageous for non-steady-state calculations, because it reduces the variation in the measured plasma glucose specific activity. The glucose system has served as the prototype, but the protocol is applicable to other blood-borne substances. The radioactive tracer case has been considered, but the same results apply to stable isotope tracers as well; in this case they also become relevant in a somewhat different context, i.e., kinetic studies in steady state.

Effects of insulin on glucose turnover rates in vivo: Isotope dilution versus constant specific activity technique

Metabolism ◽  
1996 ◽  
Vol 45 (1) ◽  
pp. 82-91 ◽  
Author(s):  
Ole Hother-Nielsen ◽  
Jan Erik Henriksen ◽  
Jens Juul Holst ◽  
Henning Beck-Nielsen
Keyword(s):  
Isotope Dilution ◽  
Specific Activity ◽  
Glucose Turnover ◽  
Turnover Rates ◽  
Constant Specific Activity

scholarly journals Benzodiazepine Receptor Quantification in vivo in Humans Using [11C]Flumazenil and PET: Application of the Steady-State Principle

1995 ◽  
Vol 15 (1) ◽  
pp. 152-165 ◽  
Author(s):  
N. A. Lassen ◽  
P. A. Bartenstein ◽  
A. A. Lammertsma ◽  
M. C. Prevett ◽  
D. R. Turton ◽  
...  
Keyword(s):  
Steady State ◽  
Specific Activity ◽  
High Specific Activity ◽  
Receptor Occupancy ◽  
Occipital Cortex ◽  
Constant Infusion ◽  
Tracer Injection ◽  
Free Concentration ◽  
The Brain

Carbon-11-labeled flumazenil combined with positron emission tomography (PET) was used to measure the concentration ( Bmax) of the benzodiazepine (Bz) receptor in the brain and its equilibrium dissociation constant ( KD) for flumazenil in five normal subjects. The steady-state approach was used injecting the tracer as a bolus of high specific activity. In each subject two studies were carried out. The first study was performed at essentially zero receptor occupancy, the tracer alone study. The second study was performed at a steady-state receptor occupancy of about 50%, achieved by a prolonged constant infusion of nonlabeled (“cold”) flumazenil starting 2 h before the bolus tracer injection and continuing until the end of the scanning period. In this second study the free concentration of unmetabolized flumazenil in plasma water was measured in multiple blood samples. The observed tissue and plasma tracer curves, calibrated in the same units of radioactivity per millimeter, were analyzed in two ways: (a) by the noncompartmental (stochastic) approach making no assumptions regarding number of compartments in the tissue, and (b) by the single-compartment approach assuming rapid exchange (mixing) of tracer between all tissue compartments. The noncompartmental and the compartmental analyses gave essentially the same values for the distribution volume of the tracer, the parameter used for quantitation of the Bz receptor. As the compartmental approach could be applied to a shorter observation period (60 min instead of 120 min) it was preferred. The five subjects had a mean KD value of 12 n M/L of water and Bmax values of the grey matter ranging from 39 ± 11 in thalamus to 120 ± 14 n M/L of brain in occipital cortex. Most previous studies have been based on the pseudoequilibrium approach using the brain stem as a receptor-free reference region. This yields practically the same KD but lower Bmax values than the steady-state approach presented here.

SPECT Quantification of [123I]Iomazenil Binding to Benzodiazepine Receptors in Nonhuman Primates: II. Equilibrium Analysis of Constant Infusion Experiments and Correlation with in vitro Parameters

1994 ◽  
Vol 14 (3) ◽  
pp. 453-465 ◽  
Author(s):  
Marc Laruelle ◽  
Anissa Abi-Dargham ◽  
Mohammed S. AI-Tikriti ◽  
Ronald M. Baldwin ◽  
Yolanda Zea-Ponce ◽  
...  
Keyword(s):  
Specific Activity ◽  
Single Photon ◽  
Benzodiazepine Receptors ◽  
Photon Emission ◽  
Benzodiazepine Receptor ◽  
Equilibrium Analysis ◽  
Constant Infusion ◽  
Scatchard Analysis

In vivo benzodiazepine receptor equilibrium dissociation constant, KD, and maximum number of binding sites, Bmax, were measured by single photon emission computerized tomography (SPECT) in three baboons. Animals were injected with a bolus followed by a constant i.v. infusion of the high affinity benzodiazepine ligand [123I]iomazenil. Plasma steady-state concentration and receptor–ligand equilibrium were reached within 2 and 3 h, respectively, and were sustained for the duration (4–9 h) of the experiments (n = 15). At the end of the experiments, a receptor saturating dose of flumazenil (0.2 mg/kg) was injected to measure nondisplaceable activity. Experiments were carried out at various levels of specific activity, and Scatchard analysis was performed for derivation of the KD (0.59 ± 0.09 n M) and Bmax (from 126 n M in the occipital region to 68 n M in the striatum). Two animals were killed and [125I]iomazenil Bmax and KD were measured at 22 and 37°C on occipital homogenate membranes. In vitro values of Bmax (114 ± 33 n M) and 37°C KD (0.66 ± 0.16 n M) were in good agreement with in vivo values measured by SPECT. This study demonstrates that SPECT can be used to quantify central neuroreceptors density and affinity.

scholarly journals In Vitro Characterization of Rabbit Thrombin, Antithrombin III, and Thrombin-Antithrombin III Complex, and Determination of Their Survival Times in Vivo

1977 ◽  
Author(s):  
Christine N. Vogel ◽  
Kingdon S. Henry ◽  
Roger L. Lundblad
Keyword(s):  
Gel Electrophoresis ◽  
Half Life ◽  
Antithrombin Iii ◽  
Specific Activity ◽  
Sodium Dodecyl ◽  
In Vivo Studies ◽  
Survival Times ◽  
At Iii

Our intention is to study the interaction of rabbit thrombin with antithrombin III (AT-III) in vitro and in vivo. After activation of crude prothrombin with tissue thromboplastin and CaCl2, thrombin was purified and showed two species of thrombin with molecular weights of 36,000 and 39,000 daltons as determined by sodium dodecyl sulfate discontinuous gel electrophoresis. Rabbit AT-III was purified using a heparin agarose column and had a molecular weight of 55,000 daltons. The inhibition of thrombin by AT-III was followed by fibrinogen clotting assays and an AT-III-thrombin complex was observed on gel electrophoresis. For the in vivo studies both thrombin and AT-III were radiolabelled with Na125i using the solid state lactoperoxidase method and retained 99% of the pre-iodinated specific activity. Radiolabelled thrombin and a radiolabelled AT-III-thrombin complex were injected into different rabbits. The rate of removal of both was very similar with a half-life of approximately 9 hours. When radiolabelled AT-III was injected, the half-life was approximately 60 hours. Since the disappearance rate of thrombin more closely approximates that of the preformed AT-III-thrombin complex and is clearly shorter than the turnover rate of AT-III, the possibility is raised that thrombin combines in vivo with a native inhibitor such as AT-III and may in fact be removed from the circulation as a complex rather than as a native molecule.

Theory of production rate calculations in steady and non-steady states and its application to glucose metabolism

1992 ◽  
Vol 262 (6) ◽  
pp. E779-E790 ◽  
Author(s):  
J. A. Jacquez
Keyword(s):  
Steady State ◽  
Experimental Design ◽  
Specific Activity ◽  
Glucose Production ◽  
Central Compartment ◽  
Correct Equation ◽  
Endogenous Production ◽  
Correction Terms ◽  
Theory Of Production ◽  
Constant Specific Activity

I present a review and synthesis of the basic theory, steady state, and non-steady state for the calculation of metabolite production rates for systems that have a central well-mixed compartment that is the site of tracer input and sampling. The theory is then applied to the calculation of glucose production. If the only inputs are into the central compartment, an experimental design that involves varying tracer infusion rates to maintain constant specific activity in the central compartment and the same constant specific activity in the peripheral compartments allows calculation of the endogenous production. That holds even if the models are unidentifiable. The correct equation and Steele's pool fraction approximation reduce to the same result for this experimental design. However, that does not justify the use of Steele's equation when there are deviations from the exact experimental design. When the specific activity in the central compartment is not constant, model-dependent correction terms to Steele's equation are needed.

scholarly journals Mutations That Confer Resistance to 2-Deoxyglucose Reduce the Specific Activity of Hexokinase from Myxococcus xanthus

1999 ◽  
Vol 181 (7) ◽  
pp. 2225-2235 ◽  
Author(s):  
Philip Youderian ◽  
Matthew C. Lawes ◽  
Chad Creighton ◽  
Jessica C. Cook ◽  
Milton H. Saier
Keyword(s):  
Specific Activity ◽  
Myxococcus Xanthus ◽  
Glucose Turnover ◽  
Enzyme Assays ◽  
Phosphotransferase System ◽  
Glucokinase Gene ◽  
Multicellular Development ◽  
Spontaneous Frequency

ABSTRACT The glucose analog 2-deoxyglucose (2dGlc) inhibits the growth and multicellular development of Myxococcus xanthus. Mutants ofM. xanthus resistant to 2dGlc, designated hexmutants, arise at a low spontaneous frequency. Expression of theEscherichia coli glk (glucokinase) gene in M. xanthus hex mutants restores 2dGlc sensitivity, suggesting that these mutants arise upon the loss of a soluble hexokinase function that phosphorylates 2dGlc to form the toxic intermediate, 2-deoxyglucose-6-phosphate. Enzyme assays of M. xanthusextracts reveal a soluble hexokinase (ATP:d-hexose-6-phosphotransferase; EC 2.7.1.1 ) activity but no phosphotransferase system activities. The hexmutants have lower levels of hexokinase activities than the wild type, and the levels of hexokinase activity exhibited by the hexmutants are inversely correlated with the ability of 2dGlc to inhibit their growth and sporulation. Both 2dGlc andN-acetylglucosamine act as inhibitors of glucose turnover by the M. xanthus hexokinase in vitro, consistent with the finding that glucose and N-acetylglucosamine can antagonize the toxic effects of 2dGlc in vivo.

scholarly journals Lessons Learned from In Vivo Studies of a Viral Noncoding RNA

mSphere ◽  
2016 ◽  
Vol 1 (2) ◽  
Author(s):  
Rodney P. Kincaid ◽  
Christopher S. Sullivan
Keyword(s):  
Noncoding Rna ◽  
Recent Article ◽  
Latent Infection ◽  
Specific Activity ◽  
Noncoding Rnas ◽  
Lessons Learned ◽  
In Vivo Studies ◽  
Viral Dissemination ◽  
Future Studies

ABSTRACT Despite increasing interest in the biology of noncoding RNAs (ncRNAs), few functions have been uncovered for viral ncRNAs in vivo. In their recent article in mSphere, Feldman and colleagues [E. R. Feldman et al., mSphere 1(2):e00105-15, 2016, doi:10.1128/mSphere.00105-15 ] demonstrate a highly specific activity of a gammaherpesviral ncRNA in viral dissemination and establishment of latent infection. Their work highlights several interesting features that should be informative to future studies of viral ncRNA.

Gastrointestinal tract, hepatic, hindlimb, and renal recovery of CO2 in vivo

2000 ◽  
Vol 89 (5) ◽  
pp. 2000-2006 ◽  
Author(s):  
Jennifer D. Gresham ◽  
Koji Okamura ◽  
Phillip E. Williams ◽  
Kareem Jabbour ◽  
Paul J. Flakoll
Keyword(s):  
Gastrointestinal Tract ◽  
Pool Size ◽  
In Vivo Studies ◽  
Whole Body ◽  
Constant Infusion ◽  
Potential Contribution ◽  
Experimental Conditions ◽  
Rate Of Decay ◽  
Total Body

Whole body oxidative rates of labeled substrates are often measured by collecting expired air and determining the amount of labeled CO2 that is produced. However, the CO2 produced may not be completely recovered under all circumstances, and there is a wide variation in values reported under different experimental conditions (∼50–100%). The potential contribution of specific organs to this variation has not been defined. In vivo studies using healthy, postabsorptive, multicatheterized conscious canines were conducted to determine gastrointestinal tract, hepatic, hindlimb, and renal recoveries of NaH14CO3 during a 180-min constant infusion [0.022 ± 0.002 (SE) μCi · kg−1 · min−1]. Before the constant infusion period, a bolus infusion of NaH14CO3 (1.76 ± 0.16 μCi/kg) was given, and the rate of decay in blood was measured over a 15-min period to determine pool size. The pool size for the distribution of14CO2 was ∼80% of the total body pool (16.0 ± 1.7 liters). Whole body recovery was 97.2 ± 6.7%. The recoveries across the liver, gut, leg, and kidney were 99.9 ± 1.3, 98.0 ± 1.4, 96.7 ± 2.6, and 99.9 ± 2.1%, respectively. In conclusion, hepatic, gastrointestinal tract, hindlimb, and renal recoveries of CO2 in vivo were near 100%, suggesting that CO2 loss is not greater in gluconeogenic organs and that corrections for incomplete recovery of CO2, when measuring oxidation of substrates across these organs under normal postabsorptive conditions, would be very minor.

Glucose transport and equilibrium across alveolar-airway barrier of rat

1996 ◽  
Vol 270 (2) ◽  
pp. L183-L190 ◽  
Author(s):  
G. Saumon ◽  
G. Martet ◽  
P. Loiseau
Keyword(s):  
Steady State ◽  
Glucose Transport ◽  
Glucose Concentration ◽  
Epithelial Lining Fluid ◽  
Uptake Sites ◽  
Maximum Uptake Rate ◽  
Isolated Lungs ◽  
Kinetics Of ◽  
State Concentration

The glucose concentration in the epithelial lining fluid (ELF) results from a balance between cellular uptake and paracellular leakage. The present study examines whether the ELF glucose concentration can be predicted from the kinetics of glucose transport obtained in fluid-filled lungs. Isolated rat lungs were filled via the trachea with instillate containing 0-10 mM glucose; the perfusate glucose concentration was 10 mM. The rate of glucose removal from airspaces depended on luminal glucose concentration and was saturable [maximum uptake rate = 101 +/- 8.6 mumol.h-1.g dry lung wt-1; apparent Michaelis constant K(m) = 1.5 +/- 0.43 mM; R2 = 0.79]. Glucose removal was inhibited by phloridzin but not by phloretin or by inhibiting glycolysis. The steady-state concentration in fluid-filled lungs was estimated to be 0.15 +/- 0.034 mM. It agreed with that (< 1/20 plasma) calculated using glucose transport kinetics and paracellular permeability. The ELF glucose concentration obtained by bronchoalveolar lavage was 0.39 +/- 0.012 plasma in vivo and 0.39 +/- 0.021 perfusate in air-filled isolated lungs. The equilibrium ELF/perfusate distribution ratio of alpha-methyl-glucose was similar to that of glucose. Thus there is a major difference between the alveolar steady-state glucose concentration in air- and fluid-filled lungs despite similar mechanisms of airspace glucose removal. This suggests that glucose kinetics or access to uptake sites differ in air- and fluid-filled lungs.

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