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  • 1
    Electronic Resource
    Electronic Resource
    No evidence for isotope discrimination of tritiated glucose tracers in measurements of glucose turnover rates in man (1990)
    Springer
    Diabetologia 33 (1990), S. 168-173 
    Details
    ISSN: 1432-0428
    Keywords: Glucose metabolism ; tritiated glucose ; hyperinsulinaemia ; radioisotope effect
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Under non-steady-state conditions, glucose turnover rates determined with tritiated glucose tracers are often underestimated. To examine whether isotope discrimination or a tracer contaminant can contribute to this, we compared the turnover rates of unlabelled and tritiated glucose under isotopic steady-state conditions. The turnover rates were measured in 20 healthy subjects at two insulin concentrations (79±3 mU·l−1 and 704±62 mU·l−1). Euglycaemia was maintained by infusing unlabelled glucose mixed with (33H)-or (63H)-glucose. In both studies, the isotopically determined glucose disposal rate was virtually identical to the exogenous glucose infusion rate (low insulin 7.66±0.48 vs 7.58±0.44 mg·kg−1·min−1, high insulin 13.36±0.74 vs 13.55±0.98 mg·kg−1·min−1). The individual values were correlated in both the low (r = 0.85, p〈0.001) and high dose insulin (r=0.81, p〈0.001) studies. Tritiated glucose specific activities were also compared in arterialized and deep venous blood across forearm tissues during the high-dose insulin infusion. Glucose specific activities were similar in arterilized and deep venous blood when analysed with HPLC and conventional methods. In summary: (1) Under isotopic steady-state conditions the turnover rates of unlabelled and labelled glucoses are similar. (2) Unlabelled and labelled glucose are handled identically across forearm tissues. (3) We found no tracer impurity in our tritiated glucose preparations. We conclude that (33H)- and (63H)-glucose tracers can be used to reliably measure glucose turnover rates in man.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00404045
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  • 2
    Electronic Resource
    Electronic Resource
    Dissociation between insulin sensitivity of glucose uptake and endothelial function in normal subjects (1996)
    Springer
    Diabetologia 39 (1996), S. 1477-1482 
    Details
    ISSN: 1432-0428
    Keywords: Keywords Blood flow ; nitric oxide ; vasodilatation ; endothelium.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Insulin increases limb blood flow in a time- and dose-dependent manner. This effect can be blocked by inhibiting nitric oxide synthesis. These data raise the possibility that insulin resistance is associated with endothelial dysfunction. To examine whether endothelial function and insulin sensitivity are interrelated we quantitated in vivo insulin-stimulated rates of whole body and forearm glucose uptake at a physiological insulin concentration (euglycaemic hyperinsulinaemic clamp, 1 mU · kg–1· min–1 insulin infusion for 2 h) and on another occasion, in vivo endothelial function (blood flow response to intrabrachial infusions of sodium nitroprusside, acetylcholine, and N-monomethyl-l-arginine) in 30 normal male subjects. Subjects were divided into an insulin-resistant (IR) and an insulin-sensitive (IS) group based on the median rate of whole body glucose uptake (31 ± 2 vs 48 ± 1 μmol · kg–1· min–1, p 〈 0.001). The IR and IS groups were matched for age, but the IR group had a slightly higher body mass index, percentage of body fat and blood pressure compared to the IS group. The IR group also had diminished insulin-stimulated glucose extraction (p 〈 0.05) compared to the IS group, while basal and insulin-stimulated forearm blood flow rates were identical. There was no difference between the IR and IS groups in the forearm blood flow response to endothelium-dependent (acetylcholine and N-monomethyl-l-arginine) or -independent (sodium nitroprusside) vasoactive drugs. In conclusion, the ability of insulin to stimulate glucose uptake at physiological insulin concentrations and endothelium-dependent vasodilatation are distinct phenomena and do not necessarily coexist. [Diabetologia (1996) 39: 1477–1482]
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001250050601
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    UDP-N-acetylglucosamine transferase and glutamine: fructose 6-phosphate amidotransferase activities in insulin-sensitive tissues (1997)
    Springer
    Diabetologia 40 (1997), S. 76-81 
    Details
    ISSN: 1432-0428
    Keywords: Keywords Hexosamines ; insulin ; glucose ; diabetes mellitus.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Glutamine:fructose 6-phosphate amidotransferase (GFA) is rate-limiting for hexosamine biosynthesis, while a UDP-GlcNAc β-N-acetylglucosaminyltransferase (O-GlcNAc transferase) catalyses final O-linked attachment of GlcNAc to serine and threonine residues on intracellular proteins. Increased activity of the hexosamine pathway is a putative mediator of glucose-induced insulin resistance but the mechanisms are unclear. We determined whether O-GlcNAc transferase is found in insulin-sensitive tissues and compared its activity to that of GFA in rat tissues. We also determined whether non-insulin-dependent diabetes mellitus (NIDDM) or acute hyperinsulinaemia alters O-GlcNAc transferase activity in human skeletal muscle. O-GlcNAc transferase was measured using 3H-UDP-GlcNAc and a synthetic cationic peptide substrate containing serine and threonine residues, and GFA was determined by measuring a fluorescent derivative of GlcN6P by HPLC. O-GlcNAc transferase activities were 2–4 fold higher in skeletal muscles and the heart than in the liver, which had the lowest activity, while GFA activity was 14–36-fold higher in submandibular gland and 5–18 fold higher in the liver than in skeletal muscles or the heart. In patients with NIDDM (n = 11), basal O-GlcNAc transferase in skeletal muscle averaged 3.8 ± 0.3 nmol/mg · min, which was not different from that in normal subjects (3.3 ± 0.4 nmol/mg · min). A 180-min intravenous insulin infusion (40 mU/m2· min) did not change muscle O-GlcNAc transferase activity in either group. We conclude that O-GlcNAc transferase is widely distributed in insulin-sensitive tissues in the rat and is also found in human skeletal muscle. These findings suggest the possibility that O-linked glycosylation of intracellular proteins is involved in mediating glucose toxicity. O-GlcNAc transferase does not, however, appear to be regulated by either NIDDM or acute hyperinsulinaemia, suggesting that mass action effects determine the extent of O-linked glycosylation under hyperglycaemic conditions. [Diabetologia (1997) 40: 76–81]
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001250050645
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    Paper (German National Licenses)
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