Impact of Duration of Infusion and Choice of Isotope Label on Isotope Recycling in Glucose Homeostasis (original) (raw)
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American Journal of Physiology-Endocrinology and Metabolism, 1998
The rates (and extent) of appearance of glucose in arterialized plasma from an oral glucose load and from liver (RaO, RaH) can be estimated in humans using radioisotopes, but estimates vary among laboratories. We investigated the use of stable isotopes and undertook 22 primed intravenous infusions ofd-[6,6-2H2]glucose with an oral load includingd-[13C6]glucose in healthy humans. The effective glucose pool volume (VS) had a lower limit of 230 ml/kg body weight (cf. 130 ml/kg commonly assumed). This VSin Steele’s one-compartment model of glucose kinetics gave a systemic appearance from a 50-g oral glucose load per 70 kg body weight of 96 ± 3% of that ingested, which compared with a theoretical value of ∼95%. Mari’s two-compartment model gave 100 ± 3%. The two models gave practically identical RaOand RaHat each point in time and a plateau in the cumulative RaOwhen absorption was complete. Less than 3% of13C was recycled to [13C3]glucose, suggesting that recycling errors were practicall...
Diabetologia, 1990
The use of 13C labelled glucose in human metabolic studies has been limited by the high cost of the tracer and the problems of measuring low ~3C isotopic abundance in plasma glucose. In the present work we describe a new gas chromatograph-isotope ratio mass spectrometer allowing the measurement of a 0.001 atom % increase in 13C abundance over baseline, on a nanomole glucose sample. Studies were performed in rats and in human subjects. The rate of glucose appearance in 24 h fasted rats using D-[1-13C] glucose as tracer and analysed by this new method was found to be 10.4 + 0.7 mg-kg-*. min-1, a value 21% lower than that found using D-[6,6-2H~] glucose as tracer (13.1_+l.lmg-kg-1min-1) analysed by classic gas chromatography-mass spectrometry. The new method was also used to trace, in combination with D-[6,6 2H2] glucose, the metabolic fate in human subjects of two oral glucose loads (0.5 g. kg-1, 1 g. kg.-*) labelled with 0.1% D-[U-13C] glucose. During the six hours following the glucose load, it was found that total glucose appearance was 0.97 + 0.04 g. kg,-/ and 1.2 + 0.04 g.kg.-1, exogenous glucose appearance was 0.51 + 0.02 g. kg .-1 and 0.84+0.04 g.kg.-1, endogenous glucose production was 0.44 _+ 0.04 g. kg-~ and 0.35 + 0.06 g. kg-t after the 0.5 and 1 g. kg.-~ load respectively. These values are similar to those reported using glucose labelled with radioactive isotopes. These results show that reliable kinetic parameters of glucose metabolism can be determined, without health hazard, in humans, at low cost, using 13C labelled glucose analysed with a new gas chromatograph-isotope ratio mass spectrometer.
Diabetes, 1989
Recent studies indicate that hydrogen-labeled glucose tracers underestimate glucose turnover in humans under conditions of high flux. The cause of this underestimation is unknown. To determine whether the error is time-, pool-, model-, or insulin-dependent, glucose turnover was measured simultaneously with [6-3 H]-, [6,6-2 H 2 ]-, and [6-14 C]glucose during a 7-h infusion of either insulin (1 mU • kg~1 • min~1) or saline. During the insulin infusion, steady-state glucose turnover measured with both [6-3 H]glucose (8.0 ± 0.5 mg k g 1 mirr 1) and [6,6-2 H 2 ]glucose (7.6 ± 0.5 mg kg-1 min~1) was lower (P < .01) than either the glucose infusion rate required to maintain euglycemia (9.8 ± 0.6 mg k g 1 min~1) or glucose turnover determined with [6-14 C]glucose and corrected for Cori cycle activity (9.8 ± 0.7 mg k g 1 min 1). Consequently "negative" glucose production rates (P < .01) were obtained with either [6-3 H]-or [6,6-2 HJbut not [6-14 C]glucose. The difference between turnover estimated with [6-3 H]glucose and actual glucose disposal (or 14 C glucose flux) did not decrease with time and was not dependent on duration of isotope infusion. During saline infusion, estimates of glucose turnover were similar regardless of the glucose tracer used. High-performance liquid chromatography of the radioactive glucose tracer and plasma revealed the presence of a tritiated nonglucose contaminant. Although the contaminant represented only 1.5% of the radioactivity in the [6-3 H]glucose infusate, its clearance was 10-fold less (P < .001) than that of [6-3 H]glucose. This resulted in accumulation in plasma, with the contaminant accounting for 16.6 ± 2.09 and 10.8 ± 0.9% of what customarily is assumed Glucose 1 mM = 18 mg/dl Insulin 1 pM = 0.139
Determination of serum glucose by isotope dilution mass spectrometry: candidate definitive method
Clinical chemistry, 1992
We report a rather simple method to determine glucose concentration in serum, using isotope dilution mass spectrometry and [13C6]glucose as internal standard. The procedure involves a single step of sample purification and the conversion of the analyte into its aldononitrile pentaacetate. The between-day and within-day contribution to total variance for a single measurement was determined by assaying Standard Reference Material (SRM) 909 serum. The method was then applied to measurement of glucose concentration in three lyophilized sera: SRM 909 and two other commercially available sera. In the two studies, the concentration of SRM 909 serum was found to be 0.8% above and 0.3% below the reported value (6.25 mmol/L), respectively; the overall coefficient of variation for determinations in all sera ranged from 0.37% to 0.56%. The precision and the accuracy of the method satisfy the requirements for a Definitive Method.
The accurate determination of serum glucose by isotope dilution mass spectrometry—two methods
Biological Mass Spectrometry, 1982
Two isctope dilution mass spectrometric methods have been developed for the determination of D-glucose in human serum. Each uses a uniformly labeled ('3C)glucose as the internal standard. The first method involves conversion of glucose into 1,2 : 5,6-di-O-isopropylidene-a-~-glucofuranose and an extensive clean-up, followed by quantitation using packed column gas chromatography mass spectrometry. In the second method, glucose is converted into a-D-glucofuranose cyclic 1,2 : 3,5-bis(butylboronate)-6-acetate. The wet chemistry work-up is simpler, but analysis by capillary gas chromatography mass spectrometry is required. Both methods exhibit excellent precision (coefficients of variation <0.3%) and provided mean values that agree within 1% for all serum pools tested.
Clinical Chemistry, 2009
The isotope-labeled intravenous glucose tolerance test (IVGTT) combined with computer modeling is widely used to derive parameters related to glucose metabolism in vivo. Most of these methods involve use of either 2 H 2 -labeled or 13 C 1 -labeled D-glucose as a tracer with GC-MS to measure the isotope enrichment. These methods are challenging, both technologically and economically. We have developed a novel approach that is suitable for labeled-IVGTT studies involving a large cohort of individuals.
European Journal of Clinical Investigation, 1992
We have minimized methodological errors in the isotope dilution technique by using stable isotope, [6,6-'H2]glucose, thus avoiding the problem of contamination of tritiated glucose tracers and, by maintaining a constant plasma tracer enrichment have reduced error due to mixing transients. Using these modifications we have calculated hepatic glucose production in 20 patients with non-insulin-dependent diabetes mellitus during low (1 mU kg-' min-') and high (8 mU kg-' min-') dose insulin infusions. Mean fasting hepatic glucose production was 14.2 f 0.8 pmol kg-' min-'. This suppressed by only 68% to 4.6k0.8 pmol kg-I min-' during the low-dose insulin infusion (plasma insulin 0.85k0.05 nmol I-') and did not suppress further during the high-dose insulin infusion (plasma insulin I435 f0.83 nmol I-'). Hepatic glucose production was significantly higher than zero throughout the study. Thus, we have found that minimization of known errors in the isotope dilution technique results in physiologically plausible and significantly positive values for hepatic glucose production indicating that the liver is resistant to insulin in patients with noninsulin-dependent diabetes mellitus.
Journal of the American College of Cardiology, 1985
Simultaneous lactate production and extraction have been previously demonstrated in the myocardium in patients with coronary artery disease. To quantitate this lactate production and determine its source, dual carbon-labeled isotope experiments were performed. L-[1,2,3-13C 3) lactate and D-[6-14 C) glucose were infused in 10 patients with significant coronary artery disease. Metabolic samples were obtained at rest and during atrial pacing. Despite net chemical myocardial lactate extraction in the 10 patients at rest and no evidence of clinical ischemia, the L-[l,2,3-13C 3 ] lactate analysis demonstrated that lactate was being released by the myocardium. During atrial pacing, seven patients did not develop clinical symptoms of ischemia, and the chemical lactate analysis showed net lactate extraction. However, tracer analysis demonstrated that there was a significant increase in the lactate released during atrial pacing (from 6.9 ± 2.3 to 16.2 ± 10.1 ILmol/min) (p < 0.05). In these seven pa-The contribution of circulating glucose to lactate production is poorly defined in the human myocardium. Numerous studies (1-9) have investigated the source of lactate production in the isolated perfu sed heart or the intact anesthetized dog. Several of these investigations (1-3) suggest that glycogen stores are an important source of the lactate produced
European Journal of Clinical Investigation, 1992
We have minimized methodological errors in the isotope dilution technique by using stable isotope, [6,6-'H2]glucose, thus avoiding the problem of contamination of tritiated glucose tracers and, by maintaining a constant plasma tracer enrichment have reduced error due to mixing transients. Using these modifications we have calculated hepatic glucose production in 20 patients with non-insulin-dependent diabetes mellitus during low (1 mU kg-' min-') and high (8 mU kg-' min-') dose insulin infusions. Mean fasting hepatic glucose production was 14.2 f 0.8 pmol kg-' min-'. This suppressed by only 68% to 4.6k0.8 pmol kg-I min-' during the low-dose insulin infusion (plasma insulin 0.85k0.05 nmol I-') and did not suppress further during the high-dose insulin infusion (plasma insulin I435 f0.83 nmol I-'). Hepatic glucose production was significantly higher than zero throughout the study.