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  • 1
    ISSN: 1432-0428
    Keywords: Glucose cycle ; insulin resistance ; Type 2 (non-insulin-dependent) diabetes mellitus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary It has been suggested that increased glucose/glucose 6-phosphate substrate cycling impairs net hepatic glucose uptake in Type 2 (non-insulin-dependent) diabetes mellitus and contributes to hyperglycaemia. To investigate glucose/glucose 6-phosphate cycle activity and insulin action in Type 2 diabetes we studied eight patients and eight healthy control subjects, using the euglycaemic glucose clamp and isotope dilution techniques with purified [2-3H]- and [6-3H] glucose tracers, in the post-absorptive state and eight patients and five healthy control subjects during consecutive insulin infusions at rates of 0.4 and 2.0 mU·kg−1·min−1. [2-3H]glucose and [6-3H]glucose radioactivity in plasma samples were determined using selective enzymatic detritiation, allowing calculation of glucose turnover rates for each isotope, the difference being glucose/glucose 6-phosphate cycling. Endogenous glucose production ([6-3H]glucose) was greater in diabetic than control subjects in the post-absorptive state (15.6±1.5 vs 11.3±0.4 μmol·kg−1·min−1, p〈0.05) and during the 0.4 mU insulin infusion (10.1±1.3 vs 5.2±0.3 μmol·kg−1·min−1, p〈0.01) indicating hepatic insulin resistance. Glucose/glucose 6-phosphate cycling was significantly greater in diabetic than in control subjects in the post-absorptive state (2.6±0.4 vs 1.6±0.2 μmol·kg−1·min−1, p〈0.05) but not during the 0.4 mU insulin infusion (2.0±0.4 vs 2.0±0.3 μmol·kg−1·min−1). During the 2.0 mU insulin infusion endogenous glucose production was suppressed to a similar degree in both groups (2.6±0.5 vs 3.4±0.7 μmol · kg−1·min−1) but glucose disappearance was lower in the diabetic subjects (30.8±2.0 vs 52.4±4.6 μmol·kg−1·min−1, p〈0.01). During the 2.0 mU insulin infusion glucose/glucose 6-phosphate cycling was greater in the diabetic subjects (3.8±0.7 vs 0.8±0.6 μmol·kg−1·min−1, p〈0.05). In conclusion, both hepatic and peripheral insulin action are impaired in Type 2 diabetes. Increased glucose/glucose 6-phosphate cycling is seen in the post-absorptive state and also during marked hyperinsulinaemia, when insulin resistance is predominantly due to reduced peripheral tissue glucose uptake.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-0428
    Keywords: Tritiated glucose ; non-steady state glucose turnover ; hyperinsulinaemic glucose clamps ; HPLC ; tracer impurity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The use of tritiated glucose tracers may result in underestimation of glucose turnover during hyperinsulinaemic clamps giving paradoxical negative endogenous glucose production rates. While mathematical modelling errors in the analysis of tracer data are major determinants of this underestimate in the non-steady state, the relative importance of tracer contamination under these conditions remains in doubt. We have used high performance liquid chromatography to assess the possible contribution to this problem of a labelled tracer impurity found in [6-3H]glucose. In conventional 4 h hyperinsulinaemic clamps performed in six normal subjects, labelled impurity increased as a percentage of the neutral plasma radioactivity fraction from 5.3±0.9% after a 2 h equilibration period (0 min) to 13.5±2.2% at 120 min and 15.4±2.4% at 240 min, as plasma glucose specific activities fell following the infusion of insulin. Negative endogenous glucose production rates were observed both at 90–120 min (−8.8±1.6μmol·kg−1min−1) and at 210–240 min (−8.5±1.4 μmol·kg−1min−1) implying a persistent underestimate in isotopically determined glucose appearance rate. Using chromatography data to correct for impurity increased glucose appearance rates by 7.9±2.1% at 120 min and 11.0±2.5% at 240 min. Purified tracer was then used for a further six clamps. When the conventional protocol was used with unlabelled glucose infusion an obvious negative error persisted only at 90–120 min. In contrast, labelled infusions gave exclusively positive values for endogenous glucose production. We conclude that a labelled impurity of [6-3H]glucose may be an important source of error in measurement of glucose turnover and endogenous glucose production in the non-steady state. Use of chromatographically pure tritiated glucose tracers is recommended.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-0428
    Keywords: Key words Insulin resistance ; hypertension ; non-insulin-dependent diabetes mellitus ; thiazide diuretic.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In conventional doses, thiazide diuretics impair glucose tolerance and decrease insulin sensitivity, making them an unpopular choice for treating diabetic patients with hypertension. However, use of low-dose thiazide diuretics may avoid the adverse metabolic effects seen with conventional doses. In a double-blind, randomised crossover study we assessed peripheral and hepatic insulin action in 13 hypertensive non-insulin-dependent diabetic patients after a 6-week placebo run-in and following two 12-week treatment periods with either low (1.25 mg) or conventional (5.0 mg) dose bendrofluazide. There were no differences between doses in their effects on systolic and diastolic blood pressure. Bendrofluazide 1.25 mg had significantly less effect on serum potassium, uric acid, fasting glucose and HbA1 c concentrations than the 5.00 mg dose. Exogenous glucose infusion rates required to maintain euglycaemia were significantly different between doses (p 〈 0.05) with conventional-dose bendrofluazide worsening peripheral insulin resistance compared to baseline (23.8 ± 2.9 vs 27.3 ± 3.5 μmol · kg− 1· min− 1, p 〈 0.05) and low-dose bendrofluazide producing no change compared to baseline (26.8 ± 3.6 vs 27.3 ± 3.5 μmol · kg− 1· min− 1, p = NS). Postabsorptive endogenous glucose production was higher on treatment with bendrofluazide 5.0 mg compared to 1.25 mg (11.7 ± 0.5 vs 10.2 ± 0.3 μmol · kg− 1· min− 1, p 〈 0.05) and suppressed to a lesser extent following insulin (4.0 ± 0.7 vs 2.0 ± 0.4 μmol · kg− 1· min− 1, p 〈 0.05). Treatment with bendrofluazide 5.0 mg increased postabsorptive endogenous glucose production compared to baseline (11.7 ± 0.5 vs 10.6 ± 0.4 μmol · kg− 1· min− 1, p 〈 0.05) whereas bendrofluazide 1.25 mg did not (10.2 ± 0.3 vs 10.6 ± 0.4 μmol · kg− 1· min− 1, p = NS). At a dose of 1.25 mg bendrofluazide is as effective as conventional doses but has less adverse metabolic effects. In contrast to conventional doses which worsen both hepatic and peripheral insulin resistance, low-dose bendrofluazide has no effect on insulin action in non-insulin-dependent diabetic subjects. [Diabetologia (1995) 38: 853–859]
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 1028-1033 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: New static high pressure measurements for room temperature solid argon to 800 kbar are in excellent agreement with one predicted from a theoretical reduction of shock wave data. The results demonstrate the agreement between shock and static techniques even in cases where shock temperatures are extremely high and a large thermal correction is required to reduce the Hugoniot to an isotherm. The results suggest that solid argon may provide a useful static pressure standard up to about 3–4 Mbar.
    Type of Medium: Electronic Resource
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  • 5
  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 4054-4060 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A compact charge coupled device (CCD) camera system has been designed and characterized for use in the six inch manipulator (SIM) at the Nova laser facility. The camera system has been designed to directly replace the 35 mm film packages currently used in SIM-based x-ray imaging diagnostics. The unit's electronic package has been constructed for small size and high thermal conductivity which reduces the overall camera size and improves its performance when operated within the vacuum environment of the Nova target chamber. Measurements of the x-ray imager's contrast transfer function (CTF) were made under a variety of operating conditions on a static x-ray Manson source using both the CCD and Kodak T-Max 3200 film as recording media. The CTF data were converted to an equivalent modulation transfer function (MTF). The MTF plots show that the microchannel plate has a uniform response within our measurement accuracy along its strips. In a direction normal to the strip, however, the MTF is reduced due to the slant angle of the pores in the MCP. The measurements show that the CCD camera has a lower MTF response than T-MAX film for all spatial frequencies and configurations measured. However, data obtained from the film exhibited reciprocity failure and border effects that are not observed in the CCD data. Measurements indicate that the signal-to-noise ratio for the CCD data is four to six times larger than that obtained with film and higher photon flux levels were recorded. The CCD-based diagnostic offers immediate access to the data, improved dynamic range, and reduced turnaround time, while eliminating the need for film development, digitization, equipment, and personnel. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Radiography techniques utilizing large-area x-ray sources (typically ≤7 keV) and pinhole-imaging gated x-ray diagnostics have long been used at the Nova laser facility. However, for targets requiring higher-energy x-ray backlighters (〉9 keV), low conversion efficiencies and pinhole losses combine to make this scheme unworkable. The technique of point projection radiography has been improved upon to make imaging at high x-ray energies feasible. In this scheme a "point" source of x-rays, usually a small diameter (≤25 μm) fiber, is illuminated with a single, 100-ps pulse from the Nova laser. A gated x-ray imager with a 500-ps electronic gate width is used to record the projected image. [K. S. Budil et al., Rev. Sci. Instrum. 67, 485 (1996).] The experimental challenges this technique presents and experimental results will be discussed. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 64 (1993), S. 1404-1406 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: For energetic x rays (hv≥3 keV), ring coded-aperture imaging gives better signal-to-noise ratio than equivalent-resolution pinhole cameras for inertial confinement fusion (ICF) targets. We have created a time-resolved ring coded-aperture microscope by combining a 4×3 array of annular apertures with a gated microchannel-plate x-ray imager. The new instrument can produce 500-ps duration sequences of images with a temporal resolution of 80 ps and a spatial resolution of 5 to 6 μm. In demonstration experiments, coded images of imploded targets directly driven by the Omega laser at the Laboratory for Laser Energetics showed the formation and dissolution of the target cores with improved detail. Contour plots of the images indicate that the laser illumination pattern is imprinted in the imploded core region. The gated ring-aperture microscope will be useful in detailed studies of ICF target hydrodynamics.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We have constructed two slightly different high-speed framing cameras for use on NOVA and the OMEGA Upgrade. Both units are based on the gating of a microchannel plate, with one detector having a pore length to diameter ratio half that of the other. We will discuss the factors limiting the temporal resolution of each detector and will compare the results of modeling with gate width measurements taken using a short-pulse laser. We will also compare time-resolved x-ray images recorded using one of these devices with data from an older (∼90 ps resolution) detector. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The picosecond electrical pulse-propagation characteristics of microchannel-plate detectors, used in diagnosing laser-driven inertial-confinement-fusion experiments, were measured with an electro-optic sampling system. We determined propagation velocity and signal distortion of the microchannel-plate microstrip, as well as its characteristic impedance and the substrate relative dielectric permittivity. These parameters are critical for proper calibration of the detectors and serve as a guide for their improved designs.
    Type of Medium: Electronic Resource
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