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PubMed1975

Kinetic properties of pyruvate kinase hybrids formed with native type L and inactivated type M subunits.

Bovine type M pyruvate kinase, which normally has hyperbolic kinetics with its substrates, was inactivated by treatment with trinitrobenzenesulfonic acid. The inactivation probably occurs through trinitrophenylation of the epsilon-amino group of a lysine residue in or near the ADP binding site. Although 90 to 95% of the enzymatic activity is lost by this treatment, the molecular weight and sedimentation coefficient of the trinitrophenylated enzyme are quite similar to values obtained with the native enzyme. The inactivated, trinitrophenylated type M pyruvate kinase was hybridized in vitro with the native bovine type L enzyme, which has sigmoidal kinetics with phosphoenolpyruvate but can be activated by fructose 1,6-diphosphate to give hyperbolic kinetics. Four enzymatically active species were produced, designated L4, L3M, L2M2, and LM3, according to their subunit composition. L4 and L3M have sigmoidal kinetics with phosphoenolpyruvate and are activated by fructose diphosphate. Little or no sigmoidicity was seen for L2M2, although this species is activated to a moderate degree by fructose diphosphate. LM3 appears to have hyperbolic kinetics and is activated only slightly by fructose diphosphate. The kinetic results obtained with hybrids containing trinitrophenylated type M subunits are quite similar to the results previously reported by Dyson and Cardenas ((1973) J. Biol. Chem. 248, 8482-8488) using native type M and type L subunits, indicating that the properties of a type L subunit are profoundly affected by the nature of the other subunits present in the tetramer. In fact, type L and type M subunits in a given hybrid seem to have similar kinetic responses toward phosphoenolpyruvate and fructose diphosphate.

Animals↗

PubMed2001

[Study on photodegradation kinetics of lomefloxacin hydrochloride aqueous solution].

AIM: To investigate the photodegradation kinetic characteristics of lomefloxacin hydrochloride aqueous solution. METHODS: The HPLC method was used to determine the photodegradation kinetic parameters of lomefloxacin hydrochloride aqueous solution (10 micrograms.mL-1) under various pH buffer solutions, various ionic strength of different ions and various dielectric constant conditions. RESULTS: With comparative regression analysis of linear fit, the photodegradation kinetic order of lomefloxacin hydrochloride aqueous solution was determined as n = 1. The lomefloxacin hydrochloride aqueous solution is most unstable at pH 5.08-9.40 and is relatively stable at pH 2.02-5.08 and 9.40-11.10. The higher the ionic strength in lomefloxacin hydrochloride aqueous solution, the higher the photodegradation kinetic rate constant is. The chloride ion has important effect on photodegradation in aqueous solution of lomefloxacin and results in producing chlorine derivative as the highest photodegradation product. As the dielectric constant of solution increased, the photodegradation kinetic rate constant was also increased. CONCLUSION: It was found that the photodegradation of lomefloxacin followed apparent first-order kinetics. The photodegradation kinetic rate was affected by pH remarkably and showed positive correlation with ionic strength and dielectric constant.

Anti-Infective Agents↗

PubMed2004

18F-FDG kinetics and gene expression in giant cell tumors.

UNLABELLED: 18F-FDG kinetics were evaluated by use of compartment and noncompartment models of giant cell tumors. The kinetic data were compared with the gene expression data for a subgroup of patients. METHODS: Nineteen patients with giant cell tumors were examined with PET and 18F-FDG, and tracer kinetics were assessed quantitatively. A 2-compartment model, including the transport constants k1-k4 as well as the vascular fraction (VB) for 18F-FDG, was used for evaluation of the data. A noncompartment model was used to calculate the fractal dimension of the 18F-FDG time-activity curve to assess the heterogeneity of the tracer kinetics. Furthermore, tumor specimens obtained from 5 patients were assessed with gene chip technology (U95A), and these data were compared with the quantitative 18F-FDG data. RESULTS: The giant cell tumors showed generally enhanced 18F-FDG uptake 1 h after tracer application, with a mean 18F-FDG standardized uptake value (SUV) of 4.8 (range, 1.8-9.4). Quantitative evaluation of tracer kinetics showed a preferential increase for 18F-FDG transport, with a mean k1 of 0.340. The vascular fraction accounted for 35% of the tumor volume and was high compared with those for other tumors, such as soft-tissue sarcomas. 18F-FDG kinetics were heterogeneous, with a fractal dimension of 1.3. Gene chip analysis showed that the expression of 137 genes (1.1%) exceeded the median expression value of the reference gene, beta2-microglobulin. The highest expression was observed for the gene for the small, leucine-rich proteoglycan I (biglycan), which is important for bone cell differentiation and proliferative activity. Correlation analysis revealed an association of 18F-FDG data with the expression of several genes. Mainly genes related to angiogenesis were associated with the compartment parameters. The SUV at 56-60 min was correlated with the expression of vascular endothelial growth factor A (angiogenesis) and cell division cycle 2 protein (proliferation). CONCLUSION: Despite their classification as benign tumors, giant cell tumors have generally enhanced 18F-FDG uptake, mainly attributable to an enhanced vascular fraction and increased 18F-FDG transport. A comparison of gene chip data and 18F-FDG kinetic data showed a close association of quantitative 18F-FDG results and the expression of genes related to angiogenesis.

Biomarkers, Tumor↗

PubMed1990

Rat brain protein kinase C. Kinetic analysis of substrate dependence, allosteric regulation, and autophosphorylation.

Kinetic studies on the interaction of protein kinase C with cations and substrates were performed and the effects of essential activators on the interaction of protein kinase C with its substrates were studied. The catalytic fragment of protein kinase C interacted with protein substrate, MgATP, and Mg2+. The dual divalent cation requirement was shown by kinetic analysis as well as by the ability of Mn2+ to substitute for Mg2+. Analysis of kinetic data based on equilibrium assumptions suggested a random order of interaction of the catalytic fragment with its substrate and Mg2+ cofactor. Activation of intact protein kinase C required Ca2+, phosphatidylserine (PS), and diacylglycerol (DAG) as essential activators. Kinetic analysis of the interaction of activators with substrates indicated that Ca2+ and PS acted to increase the activity of the enzyme without modulating the KM for MgATP; PS and Ca2+ significantly decreased the KM for histone. DAG, on the other hand, did not affect the KM for either MgATP or histone but dramatically enhanced the kcat of the enzyme. These studies allow kinetic distinction between the effects of PS and Ca2+ on the one hand and DAG on the other. The possible interference of the kinetic analysis by histone was also examined by studying the requirements for autophosphorylation of protein kinase C; autophosphorylation showed similar dependencies on PS and DAG. There were no effects of histone on the lipid dependence of protein kinase C autophosphorylation, phorbol dibutyrate binding, and inhibition of autophosphorylation by sphingosine. These studies are discussed in relation to a kinetic model of protein kinase C activation.

Adenosine Triphosphate↗

PubMed1978

Evaluation of a kinetic method for simultaneous determination of conjugated and unconjugated bilirubin.

This paper describes a fast kinetic method for the simultaneous determination of unconjugated and conjugated bilirugin in the same reaction solution. A stopped-flow mixing system with a stabilized photometer and small computer is used to mix sample and reagent rapidly and to record 250 data points during a 700-ms reaction time, and a regression program is used to resolve these kinetic data into the concentrations of unconjugated and conjugated bilirubin. Data are reported for synthetic single and two-component samples and for serum samples. Kinetic results for synthetic mixtures and serum samples are compared with results obtained by a conventional two-step procedure. Regression equations show good linearity between kinetically determined absorbance changes and concentration, good agreement between taken and found values for total, unconjugated, and conjugated bilirubin for synthetic samples in human serum albumin, and a good correlation between kinetic and equilibrium results for these species in sera. Regression slopes for kinetic vs. equilibrium assay results for total, unconjugated, and conjugated bilirubins in sera were 1.01 +/- 0.05, 1.04 +/- 0.03 and 0.91 +/- 0.04, respectively, with intercepts of 6.6,--2.7, and 3.8 micromol/liter, and standard errors of estimate of 28, 14, and 20 micromol/liter. These data reflect uncertainties in both the kinetic and equilibrium methods.

Bilirubin↗

PubMed1977

A comprehensive classification of kinetic methods of analysis used in clinical chemistry.

This paper presents a comprehensive classification of kinetic methods of analysis used in clinical chemistry. Objectives of the presentation are to place kinetic methods into perspective with other analytical appraoches, to identify concisely what is and is not a kinetic method, to group different kinetic methods into categories that identify important differences in operational and performance characteristics, and to suggest terminology that can identify the different approaches without ambiguity. In addition to these major objectives, the paper includes a brief historical development of the kinetic approach that covers the period from 1881 to the present, and discusses some current terminology that is believed to be ambiguous and misleading. I suggest that the detection step in analytical methods can be divided into two general categories, called equilibrium and kinetic methods. The kinetic methods are then subdivided into two general categories called fixed sensor-signal and variable sensor-signal methods. Each of these groups is then subdivided into one-point, two-point, and multi-point methods, which are then further subdivided according to what types of blanks are used, what variables are measured, and how the measured data are used to compute enzyme activity or analyte concentration. The paper identifies some commercial instruments that represent different approaches and briefly discusses relative merits of different approaches.

Chemistry, Clinical↗

PubMed1981

Kinetics of rat liver microsomal estrogen 2-hydroxylase. Evidence for sex differences at initial velocity conditions.

The enzyme kinetics of estrogen 2-hydroxylase from rat liver microsomes has been investigated using two radiotracer methods. The conversion of [4-14C]estradiol to [4-14C]2-hydroxyestradiol by microsomes was examined by isolation of the catechol estrogen. [6,7-3H]2-Hydroxyestradiol was prepared and added at the end of the incubation as a recovery marker for quantitation. Initial velocity conditions of less than 10% product formation were established. The enzyme kinetics for estrogen 2-hydroxylase from male rat liver follows classical Michaelis-Menten kinetics producing a linear Lineweaver-Burk plot. The apparent Km for estradiol under these conditions was 2.2 microM; the Vmax for freshly prepared microsomes was 5.0 nmol/mg/min while that for microsomes stored at -70 degrees C was 0.51 nmol/mg/min. On the other hand, estrogen 2-hydroxylase from female rat liver microsomes did not follow Michaelis-Menten kinetics and yielded a nonlinear double reciprocal plot. Analogous kinetic data were obtained with another radiotracer assay measuring the release of 3H2O from [2-3H]estradiol. Thus, the estrogen 2-hydroxylases of male and female rat liver differ in enzyme kinetic properties. The upwardly curving Lineweaver-Burk plot of the kinetic data of the female rat liver microsomes suggests that more than one binding site for estradiol may exist on this enzyme complex and/or that this particular estrogen 2-hydroxylase system exhibits cooperative effects.

Animals↗

PubMed2006

Automated combined kinetic and static perimetry: an alternative to standard perimetry in patients with neuro-ophthalmic disease and glaucoma.

OBJECTIVES: To create a fully automated, combined perimetry program consisting of a static examination and a kinetic examination, and to compare the results of this test with standard static and kinetic visual fields (VFs). METHODS: Fifty-six patients (74 eyes) undergoing neuro-ophthalmic or glaucoma evaluation who had standard static or kinetic perimetry examinations underwent the combined perimetry test. This automated, combined test, performed on the Octopus 101 perimeter, consisted of a static tendency-oriented perimetry examination and a preprogrammed kinetic examination. Three masked physician reviewers independently classified all of the VFs. The VF pairs were considered a match if the consensus descriptions of the standard and combined VFs matched. RESULTS: Thirty-seven eyes underwent evaluation for neuro-ophthalmic disease (comparison standard test, 20 static and 17 kinetic) and 37 for glaucoma (comparison standard test, 17 static and 20 kinetic). The VP pairs matched in 32 eyes (86%) in the neuro-ophthalmic group and 28 (76%) in the glaucoma group. On inspection by a fourth reviewer, many of the nonmatching VF pairs were those for which a consensus was not reached, but still conveyed similar information. Two glaucomatous eyes demonstrated central scotomata not delineated by the combined examination findings. Two subtle nasal steps were detected solely by the combined examination. The combined test ranged in time from 6 to 12 minutes per eye. CONCLUSIONS: The Octopus 101 perimeter can be used to create an automated test that combines the advantages of static and kinetic perimetry and produces equivalent results while not requiring examiner expertise.

Adolescent↗

PubMed1998

Protein folding in the landscape perspective: chevron plots and non-Arrhenius kinetics.

We use two simple models and the energy landscape perspective to study protein folding kinetics. A major challenge has been to use the landscape perspective to interpret experimental data, which requires ensemble averaging over the microscopic trajectories usually observed in such models. Here, because of the simplicity of the model, this can be achieved. The kinetics of protein folding falls into two classes: multiple-exponential and two-state (single-exponential) kinetics. Experiments show that two-state relaxation times have "chevron plot" dependences on denaturant and non-Arrhenius dependences on temperature. We find that HP and HP+ models can account for these behaviors. The HP model often gives bumpy landscapes with many kinetic traps and multiple-exponential behavior, whereas the HP+ model gives more smooth funnels and two-state behavior. Multiple-exponential kinetics often involves fast collapse into kinetic traps and slower barrier climbing out of the traps. Two-state kinetics often involves entropic barriers where conformational searching limits the folding speed. Transition states and activation barriers need not define a single conformation; they can involve a broad ensemble of the conformations searched on the way to the native state. We find that unfolding is not always a direct reversal of the folding process.

Animals↗

PubMed1998

Dynamic determination of anaerobic acetate kinetics using membrane mass spectrometry

A small, stirred, 14.4-mL tank reactor was designed to serve as a measurement cell for short-term investigation of microbial kinetics. A mass spectrometer membrane probe allowed the measurement of the dissolved gases of hydrogen, methane, oxygen, and carbon dioxide. pH was measured by an electrode and controlled by addition of acid or alkali. The highly sensitive measurement of gases with low solubility allowed rapid measurements at very low conversion. In kinetic experiments, a stepwise increase of substrate concentration (method A) and continuous feed of substrate (method B) were used, allowing quick estimation of substrate kinetics. Acetate conversion in mixed culture biofilms from a fluidized bed reactor was investigated. Substrate inhibition was found to be negligible in the concentration range studied. Experiments at various pH values showed that the undissociated acid form was the kinetic determinant. Kinetic parameters for Haldane kinetics of protons were KSH = 1.3 x 10(-5) mol m-3 and KIH = 8.1 x 10(-3) mol m-3. With free acid (HAc) as the rate determining species, the kinetic parameters for method A were KSHAc = 0.005 mol m-3 and KIHAc = 100 mol m-3 and for method B were KSHAc = 0.2 mol m-3 and KIHAc = 50 mol m-3. The maximum biomass activity occurred at around pH 6.5. Acetate was exclusively converted to methane and CO2 at pH > 6. Copyright 1998 John Wiley & Sons, Inc.

Journal Article↗

PubMed1999

Multicompartment analysis of gadolinium chelate kinetics: blood-tissue exchange in mammary tumors as monitored by dynamic MR imaging.

The blood-tissue exchange kinetics of gadopentetate were studied in 49 malignant and benign mammary tumors. Signal enhancement was monitored simultaneously in the aorta and in tumor for 10.5 minutes after the beginning of a 1 minute i.v. infusion of the contrast medium (CM). Kinetic analysis was based on a model with two compartments for systemic pharmacokinetics and up to three kinetically distinct compartments for tumor. Kinetic heterogeneity, ie, two or more compartments with different exchange rate constants in a given tumor, was found in 85% of carcinomas, 38% of fibroadenomas, and 14% of mastopathic tumors. The within-tumor average of CM exchange rates was 1.22 (0.62-1.65) min(-1) in carcinomas, 0.38 (0.26-0.60) min(-1) in fibroadenomas, and 0.16 (0. 12-0.20) min(-1) in mastopathies (median and interquartile distances). The area under the signal enhancement-time curve of the aorta varied 4.5-fold between individuals. It is concluded that individual CM kinetics in arterial blood should be taken into account when CM exchange rates between blood and tumor are to be determined and that a kinetic model for potentially malignant tumors should allow for kinetic heterogeneity.

Adenocarcinoma↗

PubMed2001

Mapping the ion kinetic energy in a helium microwave plasma orthogonal acceleration time-of-flight mass spectrometer.

The ion kinetic energy of a helium microwave plasma is studied using an orthogonal acceleration time-of-flight mass spectrometer. The ions produced in the plasma are extracted into the mass spectrometer in an 'off-cone' mode (i.e. the helium plasma plume is off the sampler cone), and enter the repelling zone in the x-direction, which is perpendicular to the flight tube. The information of ion initial kinetic energy was obtained from both theoretical calculations and experimental results. The potential influence of two x-direction steering plates (X-steering plates) on the ion energy and signal intensity was examined. The influence of gas composition on the ion kinetic energy was also investigated. The calculated results show that ions with different m/z have different velocity and kinetic energy when they enter the ion modulation zone, and lighter ions have higher velocity and lower kinetic energy. The experimental results obtained demonstrate that the ion signals of different m/z produced with an 'off-cone' sampling helium microwave plasma show similar trends as calculated with the potential difference of the X-steering plates, revealing their narrow kinetic energy distribution in the x-direction. Under typical operating conditions, the x-direction kinetic energy of ions detected mostly range from about 14.9 eV for (7)Li(+) to 16.8 eV for (208)Pb(+).

Journal Article↗

PubMed2003

Entropy evaluation using the kinetic method: is it feasible?

The kinetic method is one of the most widely used experimental techniques for the measurement of thermochemical parameters by mass spectrometry. Recently it has been realized that it can also be used to determine reaction entropies, but the validity of this approach has not been established. This Perspective evaluates kinetic method plots in cases where there is a significant entropy difference between the competing fragmentation channels (i.e. between sample and reference compounds in the dissociating cluster ion). The concept underlying this study is to calculate mass spectra theoretically, based on known thermochemical parameters and as a function of experimental conditions. This can be done accurately using the RRKM-based MassKinetics software. The resulting mass spectra are then interpreted by the kinetic method, yielding DeltaH and DeltaS values. These values are, in turn, compared with the true values used to generate the calculated mass spectra. The results show that the reaction entropy difference between sample and reference has a very large influence on kinetic method plots. This should always be considered when studying energy-dependent mass spectra (using metastable ions or low- or high-energy collision-induced dissociation (CID)), even if only DeltaH is to be determined. Kinetic method plots are not strictly linear and this becomes a serious issue in the case of small molecules showing a large entropy effect. In such cases, results obtained at a low degree of excitation are more accurate. Energy and entropy effects can be evaluated in a relatively straightforward manner: first, the apparent Gibbs energy (DeltaG(app)) and effective temperature (T(eff)) are determined from kinetic method plots (intercept and slope, respectively), obtained from experiments using various degrees of excitation. Second, the resulting DeltaG(app) is plotted against T(eff), the slope yielding DeltaS while the intercept (extrapolation to zero temperature) yields DeltaH. This data evaluation yields more accurate results than alternative methods used in the literature. The resulting DeltaH values are fairly accurate, with errors, in most cases, <4 kJ mol(-1). On the other hand, DeltaS is systematically underestimated by 20-40%. Empirically scaling DeltaS values determined by the kinetic method by 1.35 results in a DeltaS value within 20% (or 10 J mol(-1) K(-1)) of the theoretical value.

Journal Article↗

PubMed2004

Accuracy of enthalpy and entropy determination using the kinetic method: are we approaching a consensus?

There is an emerging consensus regarding the applicability of the kinetic method. All parties acknowledge that it is an approximate quantitative technique, capable of yielding not only enthalpy, but also entropy values. Opinions differ mainly on the accuracy of the results but it is agreed that the energy (effective temperature) dependence of kinetic method plots needs to be checked in all but the simplest of cases. When the 'apparent basicity' is found to depend on collision energy (and hence effective temperature), the extended kinetic method must be used. We have performed a large-scale modeling study, involving thousands of randomly selected molecular systems and a variety of experimental conditions, using exact calculations and realistic data sets. The results show that when the measured entropy difference between the two competing reaction channels is less than approximately 35 J mol(-1) K(-1), overall errors (standard deviations) of DeltaH(298) determined by the kinetic method are +/-5 kJ mol(-1); those of DeltaS(298) are +/-10 J mol(-1) K(-1). These include not only inherent errors of the kinetic method, but also errors in ion abundance measurement (5%) and inaccurate knowledge of reference compound thermochemistry (+/-2 kJ mol(-1), on average). We recommend, in general, that these errors be reported in kinetic method studies. When the measured entropy difference between the two competing fragmentation channels is large (>35 J mol(-1) K(-1)), it is likely to be significantly underestimated and errors of the kinetic method increase significantly.

Journal Article↗

PubMed1997

Dynamic Surface Tension and Adsorption Kinetics from Micellar Solutions on Planar Surfaces

A qualitative theory of the dynamic surface tension and adsorption kinetics from micellar surfactant solutions on a planar surface is developed for the kinetic-diffusive-controlled adsorption process obeying any adsorption kinetics on a planar surface and any micellization-demicellization kinetics in the bulk. The time-dependent adsorption and dynamic surface tension is obtained in an analytical form for short and long times. It is shown that the adsorption process and dynamic surface tension over a wide range of surfactant (monomer) concentrations is governed by: (I) the adsorption kinetics of monomers and micelles for short times (0 </= t </= tcr1), (II) the adsorption kinetics of monomers and micelles on a planar surface and the micellization-demicellization kinetics in the bulk, and the diffusion of monomers and micelles for intermediate times (tcr1 </= t </= tcr2), and (III) the diffusion of monomers and micelles for long times (t >/= tcr2). Formulas were derived to estimate the relaxation times tcr1, tcr2, and the parameters characterizing the adsorption process over a wide range of times. The existence of the (I), (II), and (III) regimes are justified by using the experimental data for the dynamic surface tension of a micellar Brij 58 solution.

Journal Article↗

PubMed1998

Theory and Experiment on the Measurement of Kinetic Rate Constants for Surfactant Exchange at an Air/Water Interface.

The paper focuses on the measurement of the rate constants for the kinetic steps of adsorption and desorption of surfactant between an air/water surface and the aqueous bulk sublayer adjacent to the surface. Kinetic constants are determined in nonequilibrium experiments in which either a clean surface is contacted with a bulk solution and surfactant diffuses toward and adsorbs onto the interface, or the area of an established monolayer in equilibrium with an underlying solution is changed, and surfactant exchanges between the surface and bulk. The dynamic tension change due to the surfactant exchange is measured, and compared to predictions of kinetic-diffusive transport models in order to infer the kinetic coefficients as well the diffusion coefficients. Model comparisons for highly surface active surfactants have resolved only the diffusion coefficient as the transport was found to be diffusion controlled; kinetic constants have only been established for less active materials such as alcohols or bolaform surfactants. In this study, we demonstrate that kinetics can be differentiated from diffusion in clean interface adsorption and re-equilibration if high bulk concentrations of the surfactant are used, or in re-equilibration, if the surface is compressed sufficiently. We first establish theoretically that mass transfer shifts from diffusion-limited to mixed as the bulk concentration increases in clean interface adsorption, or the surface compression is increased in re-equilibration. We then experimentally verify this idea by using the polyethoxylated surfactant C12E6 (C12H25 (OCH2CH2)6-OH) and by measuring dynamic surface tensions in clean interface adsorption and re-equilibration, respectively by the shape analysis of pendant bubbles. We find values of 6 x 10(-10) m2/s for the diffusion coefficient, and 1.4 x 10(-5) m/sec and 1.4 x 10(-4) s-1 for the adsorption and desorption rate constants, respectively, in a Frumkin kinetic formulation. While the adsorption constant is comparable to previously measured values for the less surface active surfactants, the desorption rate constant is a few orders of magnitude smaller. This indicates that the more surface active materials may have much smaller desorption rate constants than had been previously anticipated based on the studies of the less surface active materials. Copyright 1998 Academic Press.

Journal Article↗

PubMed2002

Application of a single model to study the adsorption kinetics of prednisolone on six carbonaceous materials.

The knowledge of the adsorption processes of nonelectrolytes from liquid solution on solid materials involves the study of their kinetic and equilibrium aspects as well as the understanding of their thermodynamic functions. However, in most published papers adsorption isotherms are analyzed by using the Giles classification and other proposed equations which are either empirical or based on kinetic or thermodynamic criteria. Our opinion is that both the kinetic and the equilibrium studies must be complementary and that, in general, equations describing the adsorption isotherms come from the kinetic laws governing the different partial processes which determine the global process. These kinetic laws may be derived from single models. In this paper a single model is proposed, which makes it possible to establish a kinetic law satisfactorily fitting a great number of C (concentration) vs t (time) isotherms. This model has been applied to study the adsorption process of prednisolone by six carbonaceous materials from ethanol solution, the specific adsorption rate, and the activation thermodynamic functions being calculated. The results obtained have also been used to analyze the influence of the intraparticle diffusion on the kinetics of the process.

Journal Article↗

PubMed1993

Circulatory models of intact-body kinetics and their relationship with compartmental and non-compartmental analysis.

Circulatory models for interpreting the kinetics of substances in vivo explain the kinetics of the intact body with the concepts of organ kinetics. In this paper, it is first shown that classical organ kinetic analysis is incomplete for metabolized substances, and an appropriate extension is developed. It is then discussed how the concepts of the extended organ kinetic analysis apply to circulatory models. At an organ level, it is shown that two impulse responses are necessary to characterize the organ, one relating influx and outflux, and one relating influx and uptake. The consideration of the inlet-uptake path is of fundamental importance for a correct calculation of the organ volume. It is demonstrated that the total volume is the sum of two components, the first related to the inlet-outlet path, the second to the inlet-uptake path. The first term is computable without assumptions, while the second is model-dependent. Analogous results hold at a total-body level. The relationships between circulatory models and compartmental and non-compartmental analysis are also precisely established. The significance of the non-compartmental estimate of the distribution volume is clarified. The usual strategy of compartmental modeling by which losses are placed in peripheral compartments according to a correspondence between tissues and compartments is shown to be misleading. An example concerning glucose kinetics is given. In conclusion, this paper shows that many of the dominating paradigms of organ and total-body kinetic analysis must be revised.

Humans↗