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  • 1
    ISSN: 1432-0428
    Keywords: Indirect two-site immunoradiometric assay ; human proinsulin ; insulin ; C-peptide ; diabetes ; insulinoma
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary An indirect two-site immunoradiometric assay is described for the measurement of human proinsulin in plasma. Polyethylene tubes coated with purified guinea-pig antibodies to insulin were used to extract proinsulin and insulin from plasma. Rabbit antibody to human C peptide was then added to react with the C-peptide moiety of the bound proinsulin. The uptake of this antibody was measured by the subsequent binding of125I-sheep antibody to rabbit IgG. The binding of radioactivity to the tubes was a function of the proinsulin concentration in the sample. The sensitivity of the assay was 0.006 pmol/ml. Only 200 μl of plasma was required in the assay and the125I-labelled antibody was produced from readily available reagents. The polyethylene tubes remained stable for at least 5 months after coating. The mean fasting proinsulin level was 0.009 pmol/ml in sixteen normal subjects and 0.025 pmol/ml in twelve maturity onset diabetics. Oral glucose produced an 8 fold increase in proinsulin concentration but a decline in the plasma proinsulin/insulin molar ratio. Four patients with insulinoma had extremely elevated proinsulin levels and proinsulin/insulin ratios.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-0428
    Keywords: Glucose ; insulin ; C-peptide ; glucose dependent insulinotropic polypeptide ; normal subjects ; Type 2 diabetic patients
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The effects of porcine glucose-dependent insulinotropic polypeptide given by continuous intravenous infusion in normal subjects (n=6) and Type 2 (non-insulin-dependent) diabetic patients (n=6) have been investigated. The subjects were studied on 2 separate days after overnight fasts. On each day 25 g of glucose was infused from 0–30 min plus an infusion of either porcine glucose-dependent insulinotropic polypeptide (0.75 pmol·kg−1·min−1) or control solution. During the glucose-dependent insulinotropic polypeptide infusion plasma glucose values were reduced in normal subjects from 30–60 min (p〈0.01) and in Type 2 diabetic patients at 45 and 60 min (p〈0.05). In the normal subjects insulin concentrations were greater from 10–35 min (p〈0.01) following glucose-dependent insulinotropic polypeptide infusion and peak values were increased by 123%. In the Type 2 diabetic patients following glucose-dependent insulinotropic polypeptide infusion insulin levels were increased from 4–40 min (p〈0.01) but peak values were only increased by 27%. In the normal subjects C-peptide values were greater from 25–45 min (p〈0.01) following glucose-dependent insulinotropic polypeptide infusion and peak C-peptide levels were increased by 82%. In the Type 2 diabetic patients following the glucose-dependent insulinotropic polypeptide infusion C-peptide levels were increased from 6–55 min (p〈0.01) and peak values were increased by 20%. Plasma glucose-dependent insulinotropic polypeptide levels were within the physiological post prandial range during the glucose-dependent insulinotropic polypeptide infusion. Glucose-dependent insulinotropic polypeptide is insulinotropic in normal subjects and Type 2 diabetic patients at physiological concentrations and results in improved glucose tolerance. This insulinotropic effect is less marked in the diabetic patients and may represent insensitivity of the B cell to glucose-dependent insulinotropic polypeptide.
    Type of Medium: Electronic Resource
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