The Experts below are selected from a list of 270 Experts worldwide ranked by ideXlab platform
H Becknielsen - One of the best experts on this subject based on the ideXlab platform.
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effects of insulin on glucose turnover rates in vivo Isotope Dilution versus constant specific activity Technique
Metabolism-clinical and Experimental, 1996Co-Authors: Ole Hothernielsen, Jan Erik Henriksen, Jens J Holst, H BecknielsenAbstract:The conventional Isotope Dilution Technique was compared with the more accurate constant specific activity (SA) method at six different insulin levels. Paired euglycemic clamp studies were performed in 30 normal subjects (4-hour insulin infusion: 5, 10, 20, 40, 80, and 160 mU . m-2 . min-1) using primed-constant 3-3H-glucose infusion and either conventional unlabeled glucose infusates (Cold-GINF) or labeled glucose infusates (Hot-GINF) to maintain constant SA. At all insulin levels, both glucose disappearance (Rd) and hepatic glucose production (HGP) were underestimated by the conventional Technique, and errors during the first 2 hours correlated with glucose infusion rates (GIRs) (r = .93, P < .00001). During the second hour, mean underestimation of HGP varied from 20% +/- 9% to 84% +/- 16% of basal rates from low-dose to high-dose insulin infusion studies. During prolonged equilibration (3 to 4 hours), errors decreased but were still significant in the two low-dose insulin infusion protocols during the fourth hour. In conclusion, using the conventional Isotope Dilution Technique, suppression of glucose production was overestimated and stimulation of glucose Rd was underestimated, and these errors were greater the higher the GIR. Thus, artifactually greater hepatic and smaller peripheral effects may have been assumed for factors or therapies that influence insulin sensitivity in previous studies using a conventional Isotope Dilution Technique, and therefore, reevaluation of these issues may be relevant in future studies.
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effects of insulin on glucose turnover rates in vivo Isotope Dilution versus constant specific activity Technique
Metabolism-clinical and Experimental, 1996Co-Authors: Ole Hothernielsen, Jan Erik Henriksen, Jens J Holst, H BecknielsenAbstract:Abstract The conventional Isotope Dilution Technique was compared with the more accurate constant specific activity (SA) method at six different insulin levels. Paired euglycemic clamp studies were performed in 30 normal subjects (4-hour insulin infusion: 5, 10, 20, 40, 80, and 160 mU · m −2 · min −1 ) using primed-constant 3- 3 H-glucose infusion and either conventional unlabeled glucose infusates (Cold-GINF) or labeled glucose infusates (Hot-GINF) to maintain constant SA. At all insulin levels, both glucose disappearance (R d ) and hepatic glucose production (HGP) were underestimated by the conventional Technique, and errors during the first 2 hours correlated with glucose infusion rates (GIRs) ( r = .93, P d was underestimated, and these errors were greater the higher the GIR. Thus, artifactually greater hepatic and smaller peripheral effects may have been assumed for factors or therapies that influence insulin sensitivity in previous studies using a conventional Isotope Dilution Technique, and therefore, reevaluation of these issues may be relevant in future studies.
Ole Hothernielsen - One of the best experts on this subject based on the ideXlab platform.
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effects of insulin on glucose turnover rates in vivo Isotope Dilution versus constant specific activity Technique
Metabolism-clinical and Experimental, 1996Co-Authors: Ole Hothernielsen, Jan Erik Henriksen, Jens J Holst, H BecknielsenAbstract:The conventional Isotope Dilution Technique was compared with the more accurate constant specific activity (SA) method at six different insulin levels. Paired euglycemic clamp studies were performed in 30 normal subjects (4-hour insulin infusion: 5, 10, 20, 40, 80, and 160 mU . m-2 . min-1) using primed-constant 3-3H-glucose infusion and either conventional unlabeled glucose infusates (Cold-GINF) or labeled glucose infusates (Hot-GINF) to maintain constant SA. At all insulin levels, both glucose disappearance (Rd) and hepatic glucose production (HGP) were underestimated by the conventional Technique, and errors during the first 2 hours correlated with glucose infusion rates (GIRs) (r = .93, P < .00001). During the second hour, mean underestimation of HGP varied from 20% +/- 9% to 84% +/- 16% of basal rates from low-dose to high-dose insulin infusion studies. During prolonged equilibration (3 to 4 hours), errors decreased but were still significant in the two low-dose insulin infusion protocols during the fourth hour. In conclusion, using the conventional Isotope Dilution Technique, suppression of glucose production was overestimated and stimulation of glucose Rd was underestimated, and these errors were greater the higher the GIR. Thus, artifactually greater hepatic and smaller peripheral effects may have been assumed for factors or therapies that influence insulin sensitivity in previous studies using a conventional Isotope Dilution Technique, and therefore, reevaluation of these issues may be relevant in future studies.
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effects of insulin on glucose turnover rates in vivo Isotope Dilution versus constant specific activity Technique
Metabolism-clinical and Experimental, 1996Co-Authors: Ole Hothernielsen, Jan Erik Henriksen, Jens J Holst, H BecknielsenAbstract:Abstract The conventional Isotope Dilution Technique was compared with the more accurate constant specific activity (SA) method at six different insulin levels. Paired euglycemic clamp studies were performed in 30 normal subjects (4-hour insulin infusion: 5, 10, 20, 40, 80, and 160 mU · m −2 · min −1 ) using primed-constant 3- 3 H-glucose infusion and either conventional unlabeled glucose infusates (Cold-GINF) or labeled glucose infusates (Hot-GINF) to maintain constant SA. At all insulin levels, both glucose disappearance (R d ) and hepatic glucose production (HGP) were underestimated by the conventional Technique, and errors during the first 2 hours correlated with glucose infusion rates (GIRs) ( r = .93, P d was underestimated, and these errors were greater the higher the GIR. Thus, artifactually greater hepatic and smaller peripheral effects may have been assumed for factors or therapies that influence insulin sensitivity in previous studies using a conventional Isotope Dilution Technique, and therefore, reevaluation of these issues may be relevant in future studies.
Jan Erik Henriksen - One of the best experts on this subject based on the ideXlab platform.
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effects of insulin on glucose turnover rates in vivo Isotope Dilution versus constant specific activity Technique
Metabolism-clinical and Experimental, 1996Co-Authors: Ole Hothernielsen, Jan Erik Henriksen, Jens J Holst, H BecknielsenAbstract:The conventional Isotope Dilution Technique was compared with the more accurate constant specific activity (SA) method at six different insulin levels. Paired euglycemic clamp studies were performed in 30 normal subjects (4-hour insulin infusion: 5, 10, 20, 40, 80, and 160 mU . m-2 . min-1) using primed-constant 3-3H-glucose infusion and either conventional unlabeled glucose infusates (Cold-GINF) or labeled glucose infusates (Hot-GINF) to maintain constant SA. At all insulin levels, both glucose disappearance (Rd) and hepatic glucose production (HGP) were underestimated by the conventional Technique, and errors during the first 2 hours correlated with glucose infusion rates (GIRs) (r = .93, P < .00001). During the second hour, mean underestimation of HGP varied from 20% +/- 9% to 84% +/- 16% of basal rates from low-dose to high-dose insulin infusion studies. During prolonged equilibration (3 to 4 hours), errors decreased but were still significant in the two low-dose insulin infusion protocols during the fourth hour. In conclusion, using the conventional Isotope Dilution Technique, suppression of glucose production was overestimated and stimulation of glucose Rd was underestimated, and these errors were greater the higher the GIR. Thus, artifactually greater hepatic and smaller peripheral effects may have been assumed for factors or therapies that influence insulin sensitivity in previous studies using a conventional Isotope Dilution Technique, and therefore, reevaluation of these issues may be relevant in future studies.
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effects of insulin on glucose turnover rates in vivo Isotope Dilution versus constant specific activity Technique
Metabolism-clinical and Experimental, 1996Co-Authors: Ole Hothernielsen, Jan Erik Henriksen, Jens J Holst, H BecknielsenAbstract:Abstract The conventional Isotope Dilution Technique was compared with the more accurate constant specific activity (SA) method at six different insulin levels. Paired euglycemic clamp studies were performed in 30 normal subjects (4-hour insulin infusion: 5, 10, 20, 40, 80, and 160 mU · m −2 · min −1 ) using primed-constant 3- 3 H-glucose infusion and either conventional unlabeled glucose infusates (Cold-GINF) or labeled glucose infusates (Hot-GINF) to maintain constant SA. At all insulin levels, both glucose disappearance (R d ) and hepatic glucose production (HGP) were underestimated by the conventional Technique, and errors during the first 2 hours correlated with glucose infusion rates (GIRs) ( r = .93, P d was underestimated, and these errors were greater the higher the GIR. Thus, artifactually greater hepatic and smaller peripheral effects may have been assumed for factors or therapies that influence insulin sensitivity in previous studies using a conventional Isotope Dilution Technique, and therefore, reevaluation of these issues may be relevant in future studies.
Jens J Holst - One of the best experts on this subject based on the ideXlab platform.
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effects of insulin on glucose turnover rates in vivo Isotope Dilution versus constant specific activity Technique
Metabolism-clinical and Experimental, 1996Co-Authors: Ole Hothernielsen, Jan Erik Henriksen, Jens J Holst, H BecknielsenAbstract:The conventional Isotope Dilution Technique was compared with the more accurate constant specific activity (SA) method at six different insulin levels. Paired euglycemic clamp studies were performed in 30 normal subjects (4-hour insulin infusion: 5, 10, 20, 40, 80, and 160 mU . m-2 . min-1) using primed-constant 3-3H-glucose infusion and either conventional unlabeled glucose infusates (Cold-GINF) or labeled glucose infusates (Hot-GINF) to maintain constant SA. At all insulin levels, both glucose disappearance (Rd) and hepatic glucose production (HGP) were underestimated by the conventional Technique, and errors during the first 2 hours correlated with glucose infusion rates (GIRs) (r = .93, P < .00001). During the second hour, mean underestimation of HGP varied from 20% +/- 9% to 84% +/- 16% of basal rates from low-dose to high-dose insulin infusion studies. During prolonged equilibration (3 to 4 hours), errors decreased but were still significant in the two low-dose insulin infusion protocols during the fourth hour. In conclusion, using the conventional Isotope Dilution Technique, suppression of glucose production was overestimated and stimulation of glucose Rd was underestimated, and these errors were greater the higher the GIR. Thus, artifactually greater hepatic and smaller peripheral effects may have been assumed for factors or therapies that influence insulin sensitivity in previous studies using a conventional Isotope Dilution Technique, and therefore, reevaluation of these issues may be relevant in future studies.
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effects of insulin on glucose turnover rates in vivo Isotope Dilution versus constant specific activity Technique
Metabolism-clinical and Experimental, 1996Co-Authors: Ole Hothernielsen, Jan Erik Henriksen, Jens J Holst, H BecknielsenAbstract:Abstract The conventional Isotope Dilution Technique was compared with the more accurate constant specific activity (SA) method at six different insulin levels. Paired euglycemic clamp studies were performed in 30 normal subjects (4-hour insulin infusion: 5, 10, 20, 40, 80, and 160 mU · m −2 · min −1 ) using primed-constant 3- 3 H-glucose infusion and either conventional unlabeled glucose infusates (Cold-GINF) or labeled glucose infusates (Hot-GINF) to maintain constant SA. At all insulin levels, both glucose disappearance (R d ) and hepatic glucose production (HGP) were underestimated by the conventional Technique, and errors during the first 2 hours correlated with glucose infusion rates (GIRs) ( r = .93, P d was underestimated, and these errors were greater the higher the GIR. Thus, artifactually greater hepatic and smaller peripheral effects may have been assumed for factors or therapies that influence insulin sensitivity in previous studies using a conventional Isotope Dilution Technique, and therefore, reevaluation of these issues may be relevant in future studies.
Klaus G. Heumann - One of the best experts on this subject based on the ideXlab platform.
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Isotope Dilution ICP-MS with laser-assisted sample introduction for direct determination of sulfur in petroleum products
Analytical and Bioanalytical Chemistry, 2005Co-Authors: Sergei F. Boulyga, Jens Heilmann, Klaus G. HeumannAbstract:Inductively coupled plasma Isotope Dilution mass spectrometry (ICP-IDMS) with direct laser-assisted introduction of Isotope-diluted samples into the plasma, using a laser ablation system with high ablation rates, was developed for accurate sulfur determinations in different petroleum products such as ‘sulfur-free’ premium gasoline, diesel fuel, and heating oil. Two certified gas oil reference materials were analyzed for method validation. Two different 34S-enriched spike compounds, namely, elementary sulfur dissolved in xylene and dibenzothiophene in hexane, were synthesized and tested for their usefulness in this Isotope Dilution Technique. The Isotope-diluted sample was adsorbed on a filter-paper-like material, which was fixed in a special holder for irradiation by the laser beam. Under these conditions no time-dependent spike/analyte fractionation was only observed for the dibenzothiophene spike during the laser ablation process, which means that the measured 34S/32S Isotope ratio of the Isotope-diluted sample remained constant—a necessary precondition for accurate results with the Isotope Dilution Technique. A comparison of LA-ICP-IDMS results with the certified values of the gas oil reference materials and with results obtained from ICP-IDMS analyses with wet sample digestion demonstrated the accuracy of the new LA-ICP-IDMS method in the concentration range of 9.2 μg g−1 (‘sulfur-free’ premium gasoline) to 10.4 mg g−1 (gas oil reference material BCR 107). The detection limit for sulfur by LA-ICP-IDMS is 0.04 μg g−1 and the analysis time is only about 10 min, which therefore also qualifies this method for accurate determinations of low sulfur contents in petroleum products on a routine level.
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accurate determination of element species by on line coupling of chromatographic systems with icp ms using Isotope Dilution Technique
Spectrochimica Acta Part B: Atomic Spectroscopy, 1998Co-Authors: Klaus G. Heumann, Stefan M Gallus, Gunther Radlinger, Jochen VoglAbstract:Abstract The instrumental design for coupling different liquid chromatographic systems such as ion, reversed phase, and size exclusion chromatography as well as capillary gas chromatography, with ICP-MS for the determination of element species is described. For accurate analyses obtaining ‘real time’ concentrations of chromatographic peaks, the Isotope Dilution mass spectrometric (IDMS) Technique is applied. Two different spiking modes are possible, one using species-specific and another one using species-unspecific spike solutions of Isotope-enriched labelled compounds. The species-specific mode is only possible for element species well defined in their structure and composition, for example iodate or selenite, whereas the species-unspecific mode must be applied in all cases where the structure and composition of the species is unknown, for example, for metal complexes with humic substances. For accurate determinations by the Isotope Dilution Technique the mass discrimination effect must also be taken into account. Iodate, iodide and organoiodine species, including those of humic substances, have been analysed in mineral, drinking and environmental water samples by coupling different liquid chromatographic methods with ICP-IDMS. Heavy metal complexes with humic substances in water samples of different origin have been characterized by size exclusion/ICP-IDMS. The possibilities of determining different environmental selenium species are discussed and the results for the analysis of selenite and selenate, which has been carried out by GC/ICP-IDMS after converting these species into a volatile piazselenol compound, are presented.
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determination of heavy metal complexes with humic substances by hplc icp ms coupling using on line Isotope Dilution Technique
Fresenius Journal of Analytical Chemistry, 1997Co-Authors: Jochen Vogl, Klaus G. HeumannAbstract:An Isotope Dilution mass spectrometric (IDMS) method has been developed for the simultaneous determination of the complexes of 11 heavy metals (Ag, Cd, Cu, Mo, Ni, Pb, Tl, U, W, Zn and Zr) with humic substances (HS) by coupling HPLC with ICP-MS and applying the on-line Isotope Dilution Technique. The HPLC separation was carried out with size exclusion chromatography. This HPLC/ICP-IDMS method was applied to samples from a brown water, ground water, sewage and seepage water as well as for a sample containing isolated fulvic acids. The total contents of heavy metals and of their complexes were analyzed in these samples with detection limits in the range of 5–110 ng/L. The analysis of heavy metal/HS complexes from the different waters resulted in characteristic fingerprints of the distribution pattern of heavy metals in the separated HS fractions. A comparison between the total heavy metal concentrations and their portions bound to humic substances showed distinct differences for the various metals. Simultaneous 12C detection was used for the characterization of HS complexes not identified by UV detection and for the determination of relative DOC concentrations of chromatographic peaks.
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development of an on line Isotope Dilution Technique with hplc icp ms for the accurate determination of elemental species
Fresenius Journal of Analytical Chemistry, 1994Co-Authors: Lothar Rottmann, Klaus G. HeumannAbstract:An on-line Isotope Dilution Technique has been developed for use with a high performance liquid chromatography system (HPLC) coupled to an inductively coupled plasma mass spectrometer (ICP-MS). With this method it is possible to characterize elemental species at low concentration levels and to quantify them accurately. The possibilities of this method are shown using the examples of the determination of the interactions of different molecular weight fractions of dissolved organic matter (DOM) with copper and molybdenum in a natural water sample.