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PubMed1972

Sugar Transport in Immature Internodal Tissue of Sugarcane: II. Mechanism of Sucrose Transport.

The mechanism by which sucrose is transported into the inner spaces of immature internodal parenchyma tissue of sugarcane (Saccharum officinarum L. var. H 49-5) was studied in short term experiments (15 to 300 seconds). Transport of sucrose, glucose, and fructose was each characterized by a V(max) of 1.3 mumoles/gram fresh weight.2 hours, and each of these three sugars mutually and competitively inhibited transport of the other two. When (14)C-glucose was supplied exogenously, (14)C-glucose 6-phosphate and (14)C-glucose were the first labeled compounds to appear in the tissue; no (14)C-sucrose was detected until after 60-second incubation. After 15-second incubation in (14)C-sucrose, all intracellular radioactivity was in glucose, fructose, glucose 6-phosphate, and fructose 6-phosphate; trace amounts of (14)C-sucrose were found after 30 seconds and after 5 minutes, 71% of the intracellular radioactivity was in sucrose. Although it was possible that sucrose was transported intact into the inner space and then immediately hydrolyzed, it was shown that the rate of hydrolysis under these conditions was too low to account for the rate of hexose accumulation. Pretreatment of the tissue with rabbit anti-invertase antiserum eliminated sucrose transport, but had no effect on glucose transport. Since the antibodies did not penetrate the plasmalemma, it was concluded that sucrose was hydrolyzed by an invertase in the free space prior to transport. The glucose and fructose moieties, or their phosphorylated derivatives, were then transported into the inner space and sucrose was resynthesized. No evidence for the involvement of sucrose phosphate in transport was found in these experiments.

Journal Article↗

PubMed1965

The metabolism of glucose by the rabbit lens in the presence and absence of oxygen.

1. The effect of the absence of oxygen on the metabolism of [U-(14)C]glucose by the rabbit lens has been examined. 2. Protein-free extracts of incubated lens were subjected to electrophoresis followed by chromatography on paper; radioautographs showed 10 compounds substantially labelled. In the absence of oxygen, less radioactivity appeared in glucose, sorbitol, fructose, alanine, glutamic acid, glutathione and nucleotides, and more in lactic acid, alpha-glycerophosphate and glycerol. 3. The radioactivity of lens protein was about two to four times greater after aerobic than after anaerobic incubation. 4. The radioactivity of carbon dioxide was 2- to 4-fold greater after aerobic incubation than after anaerobic incubation. 5. After aerobic incubation of the lens, the radioactivity of all the labelled compounds was higher in the outer part (cortex) than in the inner part (nucleus). 6. Free glycerol has been found to be present in the lens. Its concentration, and that of alpha-glycerophosphate, has been measured in the lens of several species of animal.

Alanine↗

PubMed1988

The determination of the local cerebral glucose utilization with the 2-deoxyglucose method.

In the adult mammalian brain, the energy metabolism is almost entirely dependent on glucose. Furthermore, a close relationship between the energy metabolism and the functional activity could be shown. Thus, the functional activity of the brain or parts thereof can be quantified by measuring the cerebral metabolic rate for glucose. Studying in vivo the fate of a radioactive labeled analogue of glucose, the 2-deoxy-D-[1-14C]glucose, and using quantitative autoradiographic techniques, it is possible to estimate the cerebral glucose utilization of every discrete brain region. The advantage of the 2-deoxyglucose method is, that the local cerebral glucose utilization represents a "metabolic encephalography" (Sokoloff 1982).

Animals↗

PubMed1984

Glucose metabolism of Treponema bryantii, an anaerobic rumen spirochete.

The pathway of glucose metabolism by Treponema bryantii, an obligately anaerobic spirochete isolated from bovine rumen contents, was studied. Washed cell suspensions of the spirochete consumed glucose and CO2 and produced equimolar amounts of acetate, formate, and succinate. Carbon dioxide was essential for glucose metabolism. Determination of radioactivity in products formed from 14C-labelled glucose and NaH14CO3 and assays of enzyme activities in cell-free extracts were used to determine the pathway of glucose metabolism. Treponema bryantii catabolized glucose to pyruvate via the Embden--Meyerhof--Parnas pathway. The spirochete used a coliform pyruvate-formate lyase to degrade pyruvate and produce formate and acetate. Succinate was formed by a pathway which involved the condensation of CO2 with pyruvate (or phospho(enol)pyruvate) formed from the breakdown of glucose.

Acetates↗

PubMed1975

Acute suppression of hepatic gluconeogenesis by glucose in the intact animal.

Within 2 h after glucose administration to fasting rats the incorporation of radioactive lactate into blood glucose and liver glycogen is decreased. Using tryptophan, which facilitates the study of gluconeogenesis prior to the phosphoenolpyruvate (PEP) carboxykinase step by increasing the level of certain hepatic metabolites, we have found that in animals fasted for 24 h glucose markedly decreased hepatic malate and aspartate concentrations without a corresponding fall in that of pyruvate, suggesting a decrease in pyruvate carboxylase activity. An inhibitor of fatty acid oxidation, 4-pentenoic acid, similarly decreased the accumulation of these intermediates, and octanoic acid significantly lessened the fall in malate and aspartate with glucose. The changes in tissue metabolite levels were consistent with inhibition of the liver pyruvate carboxylase reaction by glucose treatment, and with abolition of this inhibition by octanoate administration. Alanine and glutamate levels in the liver of tryptophan-treated animals were decreased 90 and 32%, respectively, by glucose. Thus, glucose administration in the whole animal acutely decreases gluconeogenesis by apparently inhibiting the pyruvate carboxylase step and decreasing alanine levels in the liver.

Animals↗

PubMed1997

Carbon monoxide contributes to the cytokine-induced inhibition of surfactant synthesis by human type II pneumocytes.

BACKGROUND: An increase in cyclic guanosine 3',5'-monophosphate (cGMP) due to nitric oxide generation is known to participate in the mediation of the tumor necrosis factor alpha (TNF-alpha) effect in type II cells. Because guanylyl cyclase can be activated also by carbon monoxide (CO), in this study we examined the ability of human type II pneumocytes to produce CO in the presence of cytokines and the relative contribution of this molecule to the TNF-alpha and interleukin 1 effects. DESIGN: Type II pneumocytes were isolated from cadaveric multiple-organ donors by enzymatic digestion, adherence separation of macrophages, and gradient purification. After preculture for 24 hours, cells were cultured for 24 hours in the presence or absence of TNF-alpha, interleukin 1, sodium nitroprusside, N(omega)-nitro-1-arginine, CO, hemin, zinc-protoporphyrin type IX, deferoxamine mesylate, S-adenosyl-L-methionine, alpha-tocopherol, methylene blue (a guanylyl cyclase inhibitor), 8-bromine-cGMP, and combinations of these reagents. Both CO (picomole per microgram of protein) and nitric oxide release to the medium and the cGMP (picomole per microgram of protein) content of the cells were measured. In a different set of experiments, D-glucose labeled with radioactive carbon (14C) was added to the medium, and the labeling of several lipid fractions was determined (picomole per microgram of protein). RESULTS: D-[14C]glucose incorporation into phosphatidylcholine, the main surfactant component, was selectively inhibited in the presence of cytokines, CO, sodium nitroprusside, or 8-bromine-cGMP. The inhibitory effect of TNF-alpha was partially reversed by N(omega)-nitro-L-arginine, deferoxamine, or alpha-tocopherol and totally reversed by methylene blue. Tumor necrosis factor alpha induced an increase in cGMP cell content and in the CO and nitric oxide release to the medium. Hemin increased CO and cGMP production and decreased phosphatidylcholine synthesis. Zinc-protoporphyrin type IX, an inhibitor of heme oxygenase, and all 3 antioxidants, which inhibited CO production, also antagonized the TNF-alpha effect on cGMP and phosphatidylcholine synthesis. CONCLUSIONS: Intracellular cGMP increase due to an endogenous generation of both CO and nitric oxide mediates the cytokine-induced inhibition of surfactant synthesis by type II pneumocytes. Both lipid peroxidation and heme oxygenase activity are sources for the observed CO production.

Adolescent↗

PubMed1968

The mechanism of thyrotrophin action in relation to lipid metabolism in thyroid tissue.

1. The effects of thyrotrophin in vitro on the incorporation of [(14)C]-glucose, -glycerol, -palmitate and -oleate into the lipids of thyroid tissue were examined. 2. Thyrotrophin increased the incorporation of these (14)C-labelled precursors into phosphatidylinositol specifically. 3. Thyrotrophin also increased the proportion of (14)C radioactivity from labelled glucose, glycerol, palmitate and oleate incorporated into the 1,2-diglycerides. 4. The addition of thyrotrophin to thyroid slices for 10min., after 2hr. of prelabelling with [(14)C]glycerol, also increased the proportion of (14)C radioactivity incorporated into the 1,2-diglyceride fraction. 5. After incubation of thyroid tissue with [1-(14)C]palmitate, thyrotrophin caused a two- to three-fold increase in the specific radioactivity of palmitate isolated from phosphatidylinositol and 1,2-diglycerides. In contrast, the specific radioactivity of palmitate isolated from the choline and ethanolamine phosphoglycerides, 1,3-diglycerides and triglycerides was not increased by thyrotrophin.

Animals↗

PubMed1968

Biosynthesis of intestinal mucins. Effect of puromycin on mucoprotein biosynthesis by sheep colonic mucosal tissue.

1. Surviving sheep colonic mucosal tissue incorporated l-[U-(14)C]threonine when incubated in Krebs medium III at 37 degrees in an atmosphere of oxygen, into a well-characterized mucoprotein fraction, isolated by papain digestion of the incubated scrapings. 2. Acidic hydrolysis and chromatography of the labelled mucoprotein showed that threonine was the only constituent to become labelled. In the presence of puromycin the incorporation of l-[U-(14)C]threonine was considerably diminished (6.7 and 18.5% of control in duplicate experiments). Furthermore, puromycin also decreased incorporation of radioactivity from d-[U-(14)C]-glucose (48.0 and 31.6% of control) and (35)SO(4) (2-) (21.2 and 23.6% of control) into the mucoprotein fraction. 3. In a puromycin-inhibited system, with d-[U-(14)C]-glucose, where the overall specific radioactivity of the mucoprotein was 48% of control, the labelling of the individual monosaccharide constituents (as% of control) was: N-acetylneuraminic acid, 44%; N-glycollylneuraminic acid, 61%; hexosamines, 46%; fucose, 68%; galactose, 34%.

Animals↗

PubMed1969

Study on the (14)C-glucose metabolism by Clonorchis sinensis: Paper Chromatographic Analyses in Combination with Autoradiography.

Radioactive (14)C-glucose(U) was given to Clonorchis sinensis in Tris buffer medium, in corder to trace the metabolic fate of the labelled carbon. The labelled carbon from glucose enters into intermediary metabolites and end products of anaeroblic glycolysis, Embden-Meyerhof pathway, and of aerobic Krebs cycle. These product were identified by one or two-dimensional paper chromatography in combination with autoradoigraphy. 1)The labelled metabolites detected in this experiment corresponded to pyruvic acid, latic acid, malic acid, succinic acid and fumaric acid. 2)Amino acids, such as alanine, aspartic acid, glutamic acid, valine, theronine, and serine, derived by the degradation of (14)C- glycose were also found. 3)Labelled compounds behaving like alanine, aspartic acid and glutamic acid were observed in the chroma to gram of incubation medium. 4)The preciptation which suggests a positive reaction for protein occured when absolute ethanol was added to the incubation medium.

Journal Article↗

PubMed1997

Feasibility of imaging pentose cycle glucose metabolism in gliomas with PET: studies in rat brain tumor models.

UNLABELLED: The feasibility of imaging pentose cycle (PC) glucose utilization in human gliomas with PET was explored in two rat glioma models by means of glucose radiolabeled in either the carbon-1 (C-1) or carbon-6 (C-6) position. METHODS: In vitro, monolayers of T-36B-10 glioma, tissue slices of intracerebral glioma grafts or slices of normal brain were fed [1-14C]glucose or [6-14C]glucose, and the generated [14C]CO2 was trapped to quantitate the ratio of [14C]CO2 from 14C-1 versus 14C-6. In vivo, rats bearing grafts of either T-36B-10 or T-C6 rat gliomas at six subcutaneous sites received simultaneous intravenous injections of either [1-11C]glucose and [6-14C]glucose, or [1-14C]glucose and [6-11C]glucose. Tumors were excised between 5 and 55 min postinjection to quantify tracer uptake while arterial plasma was collected to derive time-activity input curves. RESULTS: In vitro, the C-1/C-6 ratio for CO2 production from T-36B-10 monolayers was 8.8 +/- 0.4 (s.d.), in glioma slices it was 6.1 +/- 2.1 and in normal brain slices it was 1.1 +/- 0.7. PC metabolism in T-36B-10 was 1.8% +/- 0.5 of total glucose utilization. In vivo, tumor radioactivity levels normalized by plasma isotopic glucose levels showed that retained C-1 relative to C-6 radiolabeled glucose was significantly lower in both gliomas, 4.9% lower in T-36B-10 (p < 0.01) and 4.7% lower in T-C6 (p < 0.01). In an additional group of rats bearing T-36B-10 gliomas and exposed to 10 Gy of 137Cs irradiation 4 hr before isotope injection, the C-1 level was 5.6% lower than that for C-6 (p < 0.05). These results were analyzed with a model of glucose metabolism that simultaneously optimized parameters for C-1 and C-6 glucose kinetics by simulating the C-1 and C-6 tumor time-activity curves. The rate constant for loss of radiolabeled carbon from the tumors, k4, was higher for C-1 than for C-6 in all groups of rats (19% higher for T-36B-10 unirradiated, 32% for T-36B-10 irradiated and 32% for T-C6 unirradiated). CONCLUSION: Mathematical modeling, Monte Carlo simulations and construction of receiver-operator-characteristic curves show that if human gliomas have a similar fractional use of the PC, it should be measurable with PET using sequential studies with [1-11C]glucose and [6-11C]glucose.

Animals↗

PubMed1982

Inosine metabolism in the rat.

1. Uptake and subsequent metabolism of purine and ribose moieties was monitored after intravenous administration of doubly labelled inosine. 2. More than 95% was cleared from the plasma within 5 min, and 99% within 20 min. 3. Approx. 50% of the 160 mumol total was rapidly incorporated into liver and kidney. Kidney removed the greatest amount (21 mumol/g wet wt.), about 10-fold more than heart, lung or liver. Lung and heart accounted for only 3%. These tissues then lost radioactivity during the remainder of the experiment. Radioactivity in the skeletal muscle, in contrast, increased from 8% of the injected dose at 5 min to 40% at 60 min. 4. In liver, kidney, heart and lung there was a significant difference in the fate of inosine. After initial incorporation of inosine, kidney predominantly lost inosine; heart preferentially lost purines; lung preferentially lost ribose radioactivity; and in liver the ribose radioactivity was rapidly lost, whereas purine was retained. Some of the ribose moiety was metabolized to glucose, presumably in the liver, and then released into the blood. Ribose radioactivity (probably as glucose) and radioactive hypoxanthine accumulated in skeletal muscle throughout the experiment. 5. Inosine caused a rapid and prolonged increase in the blood glucose content, from 6 to 15 mM in 60 min. This was accompanied by a small increase in plasma insulin. 6. It is concluded that the purine and ribose radioactivity lost from the kidney, liver and other tissues becomes incorporated into skeletal muscle.

Animals↗

PubMed1993

Regulation of liver glycogen synthesis from [14C]glucose and [14C]lactate by portal-arterial glucose difference in the perfused rat liver.

To study effects of the portal-arterial glucose difference on the hepatic glycogenesis, the liver was isolated from fasted rats and was bivascularly perfused. Thirty-five milliliters of Krebs-Ringer buffer (pH 7.4) with 2 mM glucose, 3 mM lactate, 20 ng/ml insulin, and [1-14C]glucose or [U-14C]lactate was recirculated at flow rates of 14 ml/min via the portal vein and 7 ml/min via the hepatic artery. Glucose was continuously infused at a rate of 27.75 mumol/min into the portal (P experiment) and the arterial cannula (A experiment), and the portal-arterial glucose gradients were +1.98 and -3.96 mM. Perfusate glucose concentration was not different between the P and A experiments within 20 min. Perfusate lactate level was higher in the P experiment than in the A experiment at 20 min. Incorporation of radioactivity from [14C]glucose into glycogen was higher in the P experiment than in the A experiment (0.245 +/- 0.014%/20 min vs 0.175 +/- 0.022%/20 min, P < 0.01), and not influenced by the addition of insulin. Incorporation of 14C from [14C]lactate into glycogen was not different between the P and A experiments, and was significantly increased with the addition of insulin. This activity, in the presence of insulin, was higher in the P experiment than in the A experiment (0.490 +/- 0.028%/20 min vs 0.406 +/- 0.025%/20 min, P < 0.05). These results suggest that the portal-arterial glucose difference has an important role in the regulation of hepatic glycogenesis from exogenous glucose and gluconeogenesis.

Animals↗

PubMed1999

Metabolic and secretory response to D-fructose in pancreatic islets from adult rats injected with streptozotocin during the neonatal period.

The metabolic and secretory responses to D-glucose and/or D-fructose were measured in pancreatic islets prepared from either control rats or animals that had been injected with streptozotocin during the neonatal period (STZ rats). The STZ rats displayed higher plasma D-glucose concentrations, but lower plasma insulin concentrations, islet insulin content, as well as basal and nutrient-stimulated insulin release. This coincided with lower rates of D-[U-(14)C]hexose oxidation and D-[5-(3)H]hexose utilization. In both control and STZ rats, D-fructose failed to affect significantly the metabolism of d-glucose, while the aldohexose increased the ratio between D-[U-(14)C]fructose oxidation and D-[5-(3)H]fructose conversion to (3)HOH. Such a ratio was higher than that found with radioactive D-glucose in islets exposed to both hexoses, whether in control or STZ rats, indicating a far-from-negligible contribution of fructokinase to the phosphorylation of D-fructose. Despite these analogies between both the respective fate of D-glucose and D-fructose and the reciprocal metabolic effects of the two hexoses in islets from control and STZ rats, the secretory response to the ketohexose in islets from STZ rats was preferentially suppressed, relative to that evoked by the aldohexose. This gives support to the idea that the insulinotropic action of D-fructose may not be entirely accounted for by its nutritional value in islet cells.

Animals↗

PubMed1966

A function of the Golgi apparatus in polysaccharide synthesis and transport in the root-cap cells of wheat.

1. A radioautographic study of the cells of the root tips of wheat incubated with d-[1- or 6-(3)H]glucose has shown that labelled material is formed in the golgi apparatus of the root-cap cells. This material passed to the vesicles associated with the golgi bodies and then moved through the cytoplasm across the plasmalemma and was incorporated into the cell wall and slime layer of the tissue. 2. Analysis of the labelled material extracted from the root tips showed that the bulk of the radioactive material was polysaccharide; there were relatively small amounts of labelled lipids and protein in the tissue. 3. Starch was formed from the exogenous labelled glucose and it was located in the plastids of the cell. The synthesis of starch depended on the metabolic activity of the cells, which varied with the position of the cell in the various tissues of the root tip and with the amount of the exogenous glucose. 4. Isolation of the radioactive polysaccharides from the root tip incubated in the radioactive glucose has shown that the glucose was very rapidly incorporated into the galactosyl residues of the polymers. 5. Analysis of the radioactive polysaccharides has indicated that the material transported in the golgi vesicles is probably pectic substance. 6. A scheme for the synthesis of the storage and wall polysaccharides by separate routes and their location within the cell has been put forward.

Autoradiography↗

PubMed1978

The fate of 14C in glucose 6-phosphate synthesized from [1-14C]Ribose 5-phosphate by enzymes of rat liver.

1. Glucose 5-phosphate was synthesized from ribose 5-phosphate by an enzyme extract prepared from an acetone-dried powder of rat liver. Three rates of ribose 5-phosphate utilization were observed during incubation for 17 h. An analysis of intermediates and products formed throughout the incubation revealed that as much as 20% of the substrate carbon could not be accounted for. 2. With [1-14C]ribose 5-phosphate as substrate, the specific radioactivity of [14C]glucose 6-phosphate formed was determined at 1, 2, 5 and 30 min and 3, 8 and 17 h. It increased rapidly to 1.9-fold the initial specific radioactivity of [1-14C]ribose 5-phosphate at 3 h and then decreased to a value approximately equal to that of the substrate at 6 h, and finally at 17 h reached a value 0.8-fold that of the initial substrate [1-14C]ribose 5-phosphate. 3. The specific radioactivity of [14C]ribose 5-phosphate decreased to approx. 50% of its inital value during the first 3 h of the incubation and thereafter remained unchanged. 4. The distribution of 14C in the six carbon atoms of [14C]glucose 6-phosphate formed from [1-14C]ribose 5-phosphate at 1, 2, 5 and 30 min and 3, 8 and 17 h was determined. The early time intervals (1--30 min) were characterized by large amounts of 14C in C-2 and in C-6 and with C-1 and C-3 being unlabelled. In contrast, the later time intervals (3--17 h) were characterized by the appearance of 14C in C-1 and C-3 and decreasing amounts of 14C in C-2 and C-6. 5. It is concluded that neither the currently accepted reaction sequence for the non-oxidative pentose phosphate pathway nor the 'defined' pentose phosphate-cycle mechanism can be reconciled with the labelling patterns observed in glucose 6-phosphate formed during the inital 3 h of the incubation.

Animals↗

PubMed1968

Glycogen in human peripheral blood leukocytes. I. Characteristics of the synthesis and turnover of glycogen in vitro.

In the present paper a model system is described utilizing suspensions of peripheral blood leukocytes in which glycogen synthesis and degradation can be studied. Leukocyte suspensions containing 72-94% granulocytes were prepared essentially free of platelets and erythrocytes and consisted almost entirely of neutrophile granulocytes. Initial glycogen content averaged 7.36 +/- 2.05 mg/10(9) neutrophiles. In a glucose-free medium glycogenolysis took place with glycogen losses averaging 38% in 2 hr. When adequate glucose was added to the medium, glycogen was resynthesized to the original level. Glycogen resynthesis was studied with varying glucose "loads" to determine (a) the glucose level which was adequate for cell maintenance without utilization of glycogen stores, and (b) the glucose level which provided maximal glycogen resynthesis. With cell densities of 20-50 x 10(6)/ml the minimum glucose load which allowed maintenance of glycogen stores was 2 mg and 5.3 mg/10(9) neutrophiles for 30 and 60 min, respectively. During resynthesis with glucose-(14)C, as much as 88.9% of the intracellular radioactivity could be found in glycogen. Leukocyte glycogen was made radioactive by a "pulse" of glucose-(14)C followed by a "chase" with nonradioactive glucose. Specific activity changes in glycogen isolated during the "chase" showed that glycogen was in constant turnover. When glycogen was made radioactive by a "pulse" of glucose-(14)C and the cells placed in glucose-free medium, the specific activity of isolated glycogen fell rapidly. Thus, the most recently added glucose units of the molecule were also the first to be removed when conditions favoring synthesis were changed to conditions favoring degradation.Even though glycogen is constantly turning over, the enzymatic "machinery" for its synthesis is relatively stable and not dependent on continuous protein or RNA synthesis, as shown by experiments with puromycin and actinomycin.

Amino Acids↗

PubMed1975

Photoassimilation of acetate and metabolism of carbohydrate in Chlorobium thiosulfatophilum.

1. Washed cell suspensions of Chlorobium thiosulfatophilium form large amounts of a polyglucose in the light. Addition of acetate to the cells increases the formation of polysaccharide considerable. During incubation in the dark, polysaccharide decreases with time, and organic acids such as succinic and propionic acid are excreted into the medium. 2. Glucose isolated from cells which had photoassimilated 1-, 2-, and U-14C-acetate had a specific activity which lay between 1 and 2 times that of the acetate substrates. 3. To analyse the distribution of radioactivity in the glucose units formed during photoassimilation of 14C-acetate, 2 microbial degradations, with bakers' yeast and Zymomonas mobilis respectively, were used. The results show that acetate gives rise to carbon atoms 1 plus 2 and 5 plus 6 of glucose, wheras carbon atomes 3 plus 4 are not labelled. Further, the results indicate that glucose is not formed via the reductive pentose phosphate cycle when acetate is present.

Acetates↗

PubMed1990

Use of a new gas chromatograph isotope ratio mass spectrometer to trace exogenous 13C labelled glucose at a very low level of enrichment in man.

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 13C 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-1.min-1, a value 21% lower than that found using D-[6,6-2H2] glucose as tracer (13.1 +/- 1.1 mg.kg-1.min-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.-1) 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.-1 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.-1 and 0.35 +/- 0.06 g.kg.-1 after the 0.5 and 1 g.kg.-1 load respectively. These values are similar to those reported using glucose labelled with radioactive isotopes.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗