Compartmental model of leucine kinetics in humans

1991 ◽  
Vol 261 (4) ◽  
pp. E539-E550 ◽  
Author(s):  
C. Cobelli ◽  
M. P. Saccomani ◽  
P. Tessari ◽  
G. Biolo ◽  
L. Luzi ◽  
...  
Keyword(s):  
Stable Isotope ◽  
Compartmental Model ◽  
Linear Time ◽  
A Priori ◽  
Normal Subjects ◽  
Whole Body ◽  
Constant Infusion ◽  
Individual Subject ◽  
Domain Of Validity

The complexity of amino acid and protein metabolism has limited the development of comprehensive, accurate whole body kinetic models. For leucine, simplified approaches are in use to measure in vivo leucine fluxes, but their domain of validity is uncertain. We propose here a comprehensive compartmental model of the kinetics of leucine and alpha-ketoisocaproate (KIC) in humans. Data from a multiple-tracer administration were generated with a two-stage (I and II) experiment. Six normal subjects were studied. In experiment I, labeled leucine and KIC were simultaneously injected into plasma. Four plasma leucine and KIC tracer concentration curves and label in the expired CO2 were measured. In experiment II, labeled bicarbonate was injected into plasma, and labeled CO2 in the expired air was measured. Radioactive (L-[1-14C]leucine, [4,5-3H]KIC, [14C]bicarbonate) and stable isotope (L-[1-13C]leucine, [5,5,5-2H3]KIC, [13C]bicarbonate) tracers were employed. The input format was a bolus (impulse) dose in the radioactive case and a constant infusion in the stable isotope case. A number of physiologically based, linear time-invariant compartmental models were proposed and tested against the data. The model finally chosen for leucine-KIC kinetics has 10 compartments: 4 for leucine, 3 for KIC, and 3 for bicarbonate. The model is a priori uniquely identifiable, and its parameters were estimated with precision from the five curves of experiment I. The separate assessment of bicarbonate kinetics (experiment II) was shown to be unnecessary. The model defines masses and fluxes of leucine in the organism, in particular its intracellular appearance from protein breakdown, its oxidation, and its incorporation into proteins. An important feature of the model is its ability to estimate leucine oxidation by resolving the bicarbonate model in each individual subject. Finally, the model allows the assessment of the domain of validity of the simpler commonly used models.

Measuring whole-body actin/myosin protein breakdown in mice using a primed constant stable isotope-infusion protocol

2003 ◽  
Vol 104 (6) ◽  
pp. 585-590 ◽  
Author(s):  
Yvonne L. J. VISSERS ◽  
Maarten F. VON MEYENFELDT ◽  
Valeria B. BRAULIO ◽  
Yvette C. LUIKING ◽  
Nicolaas E. P. DEUTZ
Keyword(s):  
Stable Isotope ◽  
Total Protein ◽  
Myofibrillar Protein ◽  
Whole Body ◽  
Constant Infusion ◽  
Protein Breakdown ◽  
Net Protein ◽  
Infusion Protocol

To measure actin/myosin protein breakdown, the 24 h excretion of Nτ-methylhistidine (3MH) is used. However, in mice, this method is invalid. Therefore we have developed a liquid chromatography-MS technique to measure the tracer/tracee ratio and concentration of 3MH in plasma, enabling an in vivo primed constant infusion protocol with a deuterated stable isotope of 3MH. We tested this model by giving a primed constant infusion of L-[3-methyl-2H3]histidine, L-[phenyl-2H5]phenylalanine and L-[phenyl-2H2]tyrosine to three anaesthetized experimental groups: mice receiving saline intraperitoneally (i.p.) (CON), mice receiving saline i.p. and starved for 9 h (STA), and mice receiving lipopolysaccharide i.p. and starved for 9 h (STA + LPS). The contribution of myofibrillar to total protein breakdown was significantly lower in the STA group than the CON group (30±4% and 54±14% respectively; P<0.05), and was significantly higher in the STA + LPS group than the STA group (52±7% and 30±4% respectively; P<0.05). Whole-body myofibrillar protein breakdown, total protein breakdown, protein synthesis and net protein breakdown were not different between the groups. We conclude that this in vivo primed constant stable isotope-infusion protocol can give valuable information about the role of actin/myosin protein breakdown in mice.

scholarly journals Comprehensive assessment of post-prandial protein handling by the application of intrinsically labelled protein in vivo in human subjects

2021 ◽  
pp. 1-9
Author(s):  
Jorn Trommelen ◽  
Andrew M. Holwerda ◽  
Philippe J. M. Pinckaers ◽  
Luc J. C. van Loon
Keyword(s):  
Protein Synthesis ◽  
Amino Acid ◽  
Stable Isotope ◽  
Dietary Protein ◽  
Protein Metabolism ◽  
Muscle Protein ◽  
Human Subjects ◽  
Whole Body ◽  
Body Protein

All human tissues are in a constant state of remodelling, regulated by the balance between tissue protein synthesis and breakdown rates. It has been well-established that protein ingestion stimulates skeletal muscle and whole-body protein synthesis. Stable isotope-labelled amino acid methodologies are commonly applied to assess the various aspects of protein metabolism in vivo in human subjects. However, to achieve a more comprehensive assessment of post-prandial protein handling in vivo in human subjects, intravenous stable isotope-labelled amino acid infusions can be combined with the ingestion of intrinsically labelled protein and the collection of blood and muscle tissue samples. The combined application of ingesting intrinsically labelled protein with continuous intravenous stable isotope-labelled amino acid infusion allows the simultaneous assessment of protein digestion and amino acid absorption kinetics (e.g. release of dietary protein-derived amino acids into the circulation), whole-body protein metabolism (whole-body protein synthesis, breakdown and oxidation rates and net protein balance) and skeletal muscle metabolism (muscle protein fractional synthesis rates and dietary protein-derived amino acid incorporation into muscle protein). The purpose of this review is to provide an overview of the various aspects of post-prandial protein handling and metabolism with a focus on insights obtained from studies that have applied intrinsically labelled protein under a variety of conditions in different populations.

scholarly journals Comparison of different techniques for estimating rates of protein synthesis in vivo in healthy and bacteraemic rats

1985 ◽  
Vol 226 (1) ◽  
pp. 37-42 ◽  
Author(s):  
J J Pomposelli ◽  
J D Palombo ◽  
K J Hamawy ◽  
B R Bistrian ◽  
G L Blackburn ◽  
...  
Keyword(s):  
Protein Synthesis ◽  
Rectus Muscle ◽  
Stochastic Modelling ◽  
Whole Body ◽  
Constant Infusion ◽  
Second Phase ◽  
Sprague Dawley ◽  
Body Protein ◽  
To Receive

Previous studies have reported that use of a flooding dose of radiolabelled amino acid is a more precise technique than the constant infusion of tracer quantities for determining rates of protein synthesis in rapidly turning-over tissues in the rat. However, there has been little direct investigation comparing different methods under comparable conditions. Initially, 12 healthy male Sprague-Dawley rats, weighing approx. 100 g, were randomized to receive either a bolus intravenous injection of 100 mumol of L-leucine (containing 30 microCi of [1-14C]leucine)/100 g body wt., or a continuous 2 h tracer infusion of [14C]leucine. In the second phase of the experiment, 12 additional rats were intravenously injected with 1 × 10(8) colony-forming units of Pseudomonas aeruginosa and 16 h later randomized to receive one of two infusions described above. Total protein synthesis as well as fractional synthesis rates were determined in liver, rectus muscle and whole body. Synthesis rates measured in liver, muscle and whole body were significantly higher in bacteraemic rats than in healthy rats. The flooding-dose methodology gave significantly higher estimates of protein synthesis in the liver, skeletal muscle and whole body than did the continuous-infusion method using direct measurement of the acid-soluble fraction from the respective tissue. Indirect estimates of whole-body protein synthesis based on plasma enrichments and stochastic modelling gave the lowest values.

Kinetic analysis of zinc metabolism and its regulation in normal humans

1986 ◽  
Vol 251 (2) ◽  
pp. R398-R408 ◽  
Author(s):  
M. E. Wastney ◽  
R. L. Aamodt ◽  
W. F. Rumble ◽  
R. I. Henkin
Keyword(s):  
Compartmental Model ◽  
Additional Data ◽  
Normal Subjects ◽  
The Body ◽  
Whole Body ◽  
Zinc Metabolism ◽  
Zinc Intake ◽  
Normal Humans ◽  
Taste And Smell ◽  
Oral Supplement

Zinc metabolism was studied in 32 normal volunteers after oral (n = 25) or intravenous (n = 7) administration of 65Zn. Data were collected from the blood, urine, feces, whole body, and over the liver and thigh regions for 9 mo while the subjects consumed their regular diets (containing 10 mg Zn ion/day) and for an additional 9 mo while the subjects received an exogenous oral supplement of 100 mg Zn ion/day. Data from each subject were fitted by a compartmental model for zinc metabolism that was developed previously for patients with taste and smell dysfunction. These data from normal subjects were used to determine the absorption, distribution, and excretion of zinc and the mass of zinc in erythrocytes, liver, thigh, and whole body. By use of additional data obtained from the present study, the model was refined further such that a large compartment, which was previously determined to contain 90% of the body zinc, was subdivided into two compartments to represent zinc in muscle and bone. When oral zinc intake was increased 11-fold three new sites of regulation of zinc metabolism were identified in addition to the two sites previously defined in patients with taste and smell dysfunction (absorption of zinc from gut and excretion of zinc in urine). The three new sites are exchange of zinc with erythrocytes, release of zinc by muscle, and secretion of zinc into gut. Regulation at these five sites appears to maintain some tissue concentrations of zinc when dietary zinc increases.

scholarly journals Noninvasive Measurements of Human Brain Temperature Using Volume-Localized Proton Magnetic Resonance Spectroscopy

1997 ◽  
Vol 17 (4) ◽  
pp. 363-369 ◽  
Author(s):  
Ron Corbett ◽  
Abbot Laptook ◽  
Paul Weatherall
Keyword(s):  
Magnetic Resonance ◽  
Frontal Lobe ◽  
Mr Spectroscopy ◽  
Brain Temperature ◽  
Human Subjects ◽  
Normal Subjects ◽  
Whole Body ◽  
Resonance Spectroscopy ◽  
Noninvasive Measurements

Elucidation of the role of cerebral hyperthermia as a secondary factor that worsens outcome after brain injury, and the therapeutic application of modest brain hypothermia would benefit from noninvasive measurements of absolute brain temperature. The present study was performed to evaluate the feasibility of using 1H magnetic resonance (MR) spectroscopy to measure absolute brain temperature in human subjects on a clinical imaging spectroscopy system operating at a field strength of 1.5 T. In vivo calibration results were obtained from swine brain during whole-body heating and cooling, with concurrent measurements of brain temperature via implanted probes. Plots of the frequency differences between the in vivo MR peaks of water and N-acetyl-aspartate and related compounds (NAX), or water and choline and other trimethylamines versus brain temperature were linear over the temperature range studied (28–40°C). These relationships were used to estimate brain temperature from 1H MR spectra obtained from 10 adult human volunteers from 4 cm3-volumes selected from the frontal lobe and thalamus. Oral and forehead temperatures were monitored concurrently with MR data collection to verify normothermia in all the subjects studied. Temperatures determined using N-acetyl-aspartate or choline as the chemical shift reference did not differ significantly, and therefore results from these estimates were averaged. The brain temperature (mean ± SD) measured from the frontal lobe (37.2 = 0.6°C) and thalamus (37.7 ± 0.6°C) were significantly different from each other (paired t-test, p = 0.035). We conclude that 1H MR spectroscopy provides a viable noninvasive means of measuring regional brain temperatures in normal subjects and is a promising approach for measuring temperatures in brain-injured subjects.

scholarly journals In vivo threonine oxidation in growing pigs fed on diets with graded levels of threonine

1996 ◽  
Vol 75 (6) ◽  
pp. 825-837 ◽  
Author(s):  
N. Le Floc'h ◽  
C. Obled ◽  
B. Sève
Keyword(s):  
Specific Radioactivity ◽  
Vena Cava ◽  
Live Weight ◽  
Growing Pigs ◽  
Whole Body ◽  
Constant Infusion ◽  
Balanced Diet ◽  
Liver And Pancreas ◽  
Venous Plasma

Threonine oxidation to glycine was investigated in vivo in twelve growing pigs (27·4 kg live weight) fed on one of the following three diets with graded levels of threonine supply: a low-threonine diet (LT), a control well-balanced diet (C) or a high-threonine diet (HT), during 10h constant infusion of L-[1-13C]threonine and [2-3H]glycine in the cranial vena cava and [l-14C]glycine in the portal vein.13C-threonine and glycine enrichments and [3H]glycine and [14C]glycine specific radioactivities (SR) were determined at plateau in peripheral venous plasma, liver and pancreas. Glycine praduction rates calculated from plasma [2-3H]glycine or [1-14C]glycine SR gave similar values suggesting that [l-14C]glycine SR could be used in order to estimate whole-body glycine flux. The high pancreas [1-13C]glycine enrichment provided evidence that the pancreas may be, with the liver, a major site of threonine oxidation to glycine. Moreover, the present findings suggest that threonine transport into the Liver could be the limiting step of threonine oxidation in this tissue when dietary threonine supply is low. Total threonine oxidation to glycine, calculated from plasma values of enrichment and specific radioactivity, was low and constant when the estimated absorbed threonine was lower than 4 g/d and increased for higher amounts of absorbed threonine.

scholarly journals A Kinetic Method for the Measurement of Zinc Influx In Vivo in the Rainbow Trout, and the Effects of Waterborne Calcium on Flux Rates

1989 ◽  
Vol 142 (1) ◽  
pp. 425-446 ◽  
Author(s):  
D. J. SPRY ◽  
C. M. WOOD
Keyword(s):  
Rainbow Trout ◽  
Plasma Sample ◽  
Kinetic Method ◽  
Whole Body ◽  
Constant Infusion ◽  
Linear Component ◽  
Experimental Apparatus ◽  
Body Counting ◽  
Whole Body Counting

Three methods were evaluated to measure rate of influx of Zn into rainbow trout. The first two, disappearance of 65Zn from the water and whole-body counting, overestimated influx when compared with a third method which used a terminal plasma sample to calculate influx. The cause of the overestimate was a short-term adsorption phenomenon to both the experimental apparatus and the exterior of the fish. The third method measured only Zn which entered the fish. This method entailed ‘calibration’ of cannulated trout by constant infusion of small amounts of radiolabelled Zn. This was analogous to the entry of Zn into fish across the gill. After 24–36 h of infusion, plasma radioactivity reached a steadystate concentration which was a simple linear function of the rate of infusion. This relationship was then used to predict influx from a single terminal plasma sample from uncannulated trout exposed to radiolabelled Zn in the water. Trout acclimated to tapwater (Ca2+ = 2.0 mequivl−1) and exposed to Zn (1.5-45.9 μequivl−1; 0.05-1.5 mgl−1) showed saturable uptake which was apparently first order with no significant linear component. The apparent Jmax and Km were 314 nequiv kg−1 h−1 and 7.3 μequivl−1 (0.24 mgl−1), respectively. Acutely raising the waterborne [Ca2+] (4.7 and 9.7 mequivl−1) over the same range of [Zn] revealed a competitive type of interaction - little change in Jmax, with increased Km. When Ca2+ was acutely removed (0.05 and 1.02 mequivl−1) by the use of artificial soft water, significant linear influx occurred in addition to the saturable uptake noted at higher [Ca2+], suggesting the opening of a paracellular leak. Calculation of the inhibitor constant for Ca2+ yielded a value of 0.48 mequivl−1. This value is similar to the Km for Ca2+ when it was a transported substrate (0.28 ± 0.07 mequivl−1). The true Km for Zn transport in the absence of Ca2+ was 1.0 μequivl−1 (0.06 mgl−1). These data showed Zn influx to be saturable and strongly dependent upon waterborne [Ca2+], perhaps traversing the gill in a manner similar to Ca2+.

Kinetic model of whole-body vanadium metabolism: studies in sheep

1986 ◽  
Vol 251 (2) ◽  
pp. R325-R332 ◽  
Author(s):  
B. W. Patterson ◽  
S. L. Hansard ◽  
C. B. Ammerman ◽  
P. R. Henry ◽  
L. A. Zech ◽  
...  
Keyword(s):  
Steady State ◽  
Gastrointestinal Tract ◽  
Kinetic Model ◽  
Rate Constants ◽  
Compartmental Model ◽  
Control Diet ◽  
Whole Body ◽  
Future Studies ◽  
Upper Gastrointestinal

A compartmental model for vanadium metabolism in sheep has been proposed. The model is consistent with data obtained from sheep fed a control diet (2.6 ppm vanadium) containing 0 or 200 ppm supplemental vanadium. Sheep were administered 48V dioxovanadium either orally or intravenously. Blood, feces, and urine radioactivity were monitored for 6 days postdosing. Several new insights regarding vanadium metabolism are suggested and tested against the data using the model. Some of these include significant absorption of 48V occurs from the upper gastrointestinal tract; an in vivo process is necessary in order for 48V dioxovanadium to be converted into a more biologically reactive species; at steady state the upper and lower gastrointestinal tracts contain at least 10- and 100-fold more mass of vanadium, respectively, than does blood. No statistically significant differences in transport rate constants were found between animals receiving 0 and 200 ppm supplemental dietary vanadium. The availability of a model will enable the refinement of future studies regarding vanadium metabolism in the ruminant.

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.

scholarly journals The contribution of phenylalanine to tyrosine metabolism in vivo. Studies in the post-absorptive and phenylalanine-loaded rat

1983 ◽  
Vol 210 (3) ◽  
pp. 811-817 ◽  
Author(s):  
L L Moldawer ◽  
I Kawamura ◽  
B R Bistrian ◽  
G L Blackburn
Keyword(s):  
In Vivo Studies ◽  
Whole Body ◽  
Constant Infusion ◽  
Substantial Contribution ◽  
Oxidation Rates ◽  
Plasma Phenylalanine ◽  
Tyrosine Oxidation ◽  
Tyrosine Metabolism ◽  
Plasma Tyrosine

1. Rates of appearance and oxidation of plasma L-leucine, L-phenylalanine and L-tyrosine, as well as conversion of plasma phenylalanine into plasma tyrosine, were determined in 90-120 g rats after overnight starvation and while receiving 115-120 mumol of L-phenylalanine/h. 2. In the post-absorptive state, plasma tyrosine and phenylalanine appearances were similar, despite the fact that 22% of plasma tyrosine appearance could be attributed to the hydroxylation of phenylalanine. 3. A constant infusion of 115-120 mumol of L-phenylalanine/h did not significantly alter plasma leucine kinetics, but increased appearance of plasma phenylalanine and tyrosine. The percentage of phenylalanine and tyrosine appearance that was oxidized increased from 12.1% and 24.4% to 37.3% and 48.0% respectively. In phenylalanine-loaded rats, 72% of plasma tyrosine appearance could be attributed to the conversion of phenylalanine. 4. Whole-body tyrosine oxidation measured from a continuous infusion of either L-[14C]tyrosine or L-[14C]phenylalanine differed by 165%. 5. It can be concluded that, in the post-absorptive state, phenylalanine hydroxylation makes a substantial contribution to the plasma appearance of tyrosine and is significantly increased when phenylalanine is administered. The disposal of excess infused phenylalanine is a result of a greater percentage of plasma phenylalanine being converted into tyrosine and a greater proportion of tyrosine being further oxidized. However, apparent tyrosine oxidation rates estimated from plasma tyrosine specific radioactivities and appearance of expired 14CO2 during administration of [14C]tyrosine are underestimates of true rates, in part because tyrosine generated from phenylalanine hydroxylation is catabolized without freely equilibrating with the plasma compartment.

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