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  • 1
    Electronic Resource
    Electronic Resource
    Plasma proinsulin, C-peptide and insulin in diagnostic suppression tests for insulinomas (1977)
    Springer
    Diabetologia 13 (1977), S. 571-577 
    Details
    ISSN: 1432-0428
    Keywords: Insulinoma ; malignant insulinoma ; proinsulin ; C-peptide ; insulin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The value of plasma insulin, human C-peptide and proinsulin estimation in the diagnosis of 15 insulinomas has been investigated. Measurement of plasma proinsulin in an overnight fasting sample diagnosed all the insulinomas studied, irrespective of the plasma glucose. Patients with insulinomas had plasma proinsulin in the range 0.04–4.2 pmol/l and normal values were less than 0.01 pmol/ml. If hypoglycaemia was present, an inappropriately raised plasma immunoreactive insulin (including proinsulin) was diagnostic, but this assay was of little assistance if the plasma glucose was normal. Hypoglycaemia was induced with fish insulin in twelve patients with insulinomas and eight normal subjects. Using an antiserum which did not detect fish insulin, but cross-reacted with human proinsulin, the endogenous immunoreactive insulin was suppressed in the normal subjects, but all insulinoma patients had impaired suppression. Assay of plasma human C-peptide, or of the combined immunoreactive C-peptide and proinsulin, discriminated less well and did not clearly diagnose three insulinomas which secreted proinsulin rather than insulin and C-peptide. Plasma human proinsulin values during induced hypoglycaemia gave excellent discrimination and should detect insulinomas irrespective of their degree of histological differentiation. The assay of plasma human proinsulin allows a suppression test to be performed with hypoglycaemia induced by any type of insulin. A raised plasma proinsulin in proportion to C-peptide suggests an undifferentiated insulinoma, which may be more likely to be malignant.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01236309
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  • 2
    Electronic Resource
    Electronic Resource
    Control of pulsatile insulin secretion in man (1983)
    Springer
    Diabetologia 24 (1983), S. 231-237 
    Details
    ISSN: 1432-0428
    Keywords: Insulin ; Type 2 diabetes ; oscillations ; pulsations ; man ; vagotomy ; pacemaker ; atropine ; naloxone ; phentolamine ; propranolol ; glucose ; tolbutamide ; sodium salicylate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Plasma insulin and glucose concentrations were examined in man in a basal state from central venous samples taken at 1-min intervals for up to 2.5 h. Normal subjects have insulin oscillations of mean period 14 min (significant autocorrelation, p 〈 0.0001) with changes in concentration of 40% over 7 min. The pulsation frequency was stable through cholinergic, endorphin, α-adrenergic or β-adrenergic blockade, or small pertubations with glucose or insulin. Stimulation of insulin secretion by intravenous glucose, tolbutamide or sodium salicylate increased the amplitude of the insulin oscillations while the frequency remained stable. Patients with a truncal vagotomy or after Whipple's operation had longer-term oscillations of 33 and 37 min periodicity (autocorrelation: p 〈 0.0001), with insulin-associated glucose swings four times larger than those of normal subjects. Type 2 (non-insulin-dependent) diabetic patients had a similarly increased insulin-associated glucose swing of six times that seen in normal subjects. The hypothesis is proposed that the 14-min cycle of insulin production is controlled by a ‘pacemaker’ which assists glucose homeostasis. The longer 33–37-min oscillations, seen in those with denervation, may arise from a limit-cycle of the feedback loop between insulin from the B cells and glucose from the liver. The vagus may provide hierarchical control of insulin release.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00282705
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  • 3
    Electronic Resource
    Electronic Resource
    Twenty-four hour profiles of plasma C-peptide in Type 1 (insulin-dependent) diabetic children (1982)
    Springer
    Diabetologia 22 (1982), S. 245-249 
    Details
    ISSN: 1432-0428
    Keywords: Type 1 diabetes ; diabetic children ; blood glucose profiles ; insulin ; C-peptide ; B cell
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Twenty-four hour profiles of plasma C-peptide an index of endogenous insulin secretion, were performed in 15 Type 1 (insulin-dependent) diabetic children. Plasma C-peptide was detectable in six children, of whom four (‘C-peptide producers’) had peak values above normal fasting levels. In each of the six children with residual B cell function, there was a close correlation between plasma C-peptide and simultaneous blood glucose (r〉 0.50, p〈 0.05). Post-breakfast peak blood glucose was 10.2 ± 1.7 mmol/l (mean ±SEM) in the ‘C-peptide producers’ and 18.7 ± 1.7 mmol/l in the 11 children with low or no detectable C-peptide. Mean M-value, an index of deviation from an ideal blood glucose, was lower in the ‘C-peptide producers’ (p〈0.05). It is concluded that residual functioning B cells in diabetic children behave physiologically in that insulin secretion fluctuates in accordance with the prevailing blood glucose; and that the pattern of action of injected insulin is more critical in non-C-peptide producers who lack the post-prandial dampening effect provided by residual endogenous insulin secretion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00281299
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  • 4
    Electronic Resource
    Electronic Resource
    Haemolysis affects insulin but not C-peptide immunoassay (1987)
    Springer
    Diabetologia 30 (1987), S. 394-396 
    Details
    ISSN: 1432-0428
    Keywords: Insulin ; C-peptide ; radio-immunoassay ; haemolysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Venous blood was taken at the end of a glucose infusion test in 19 individuals and divided into four aliquots, 3 of which were variably haemolysed by repeated passage through a 23-gauge needle to simulate traumatic venepuncture. Plasma insulin (measured by both a charcoal separation and a double-antibody method), C-peptide, and haemoglobin were measured in each aliquot, and haemolysis was also assessed visibly. A significant loss of immuno-assayable plasma insulin was found in samples with only a trace of visible haemolysis, with up to 90% lost in severely haemolysed samples. Plasma C-peptide was unaffected by haemolysis. This represents an additional advantage for the use of plasma C-peptide in assessing insulin secretion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00292540
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  • 5
    Electronic Resource
    Electronic Resource
    Sulphonylurea therapy doubles B-cell response to glucose in Type 2 diabetic patients (1985)
    Springer
    Diabetologia 28 (1985), S. 809-814 
    Details
    ISSN: 1432-0428
    Keywords: Sulphonylureas ; insulin ; C-peptide ; insulin resistance ; hyperglycaemic clamp
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The effect of sulphonylurea therapy for 3 weeks on glucose-stimulated insulin secretion and insulin resistance was studied in Type 2 diabetic patients. The fasting plasma insulin and C-peptide concentrations on diet alone were compared with each subject's fasting concentrations on sulphonylurea treatment at a lower fasting plasma glucose and at the original diet-alone glycaemic level obtained by the hyperglycaemic clamp technique. At this isoglycaemic level (mean 11 mmol/l), plasma insulin levels increased from 6.9 mU/l on diet alone to 12.1 mU/l on sulphonylurea treatment (p〈0.01). The subjects were also studied by the hyperglycaemic clamp technique at mean glycaemic levels of 13 mmol/l before and after sulphonylurea treatment; the incremental insulin response was similarly enhanced from 7.6±3.5 to 13.7±6.9 mU/l (p〈0.02) respectively. Sulphonylureas appear to reduce glycaemia by enhancing B-cell function two-fold. In the patients studied this was from approximately 21% to 37% of a normal response. Insulin resistance assessed by the same hyperglycaemic clamps as endogenous plasma insulin concentrations divided by glucose infusion rates was unchanged by sulphonylurea therapy (mean 4.37 compared to 4.40 mU. 1−1·mg−1·kg·min on diet alone).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00291069
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  • 6
    Electronic Resource
    Electronic Resource
    Continuous infusion of glucose with model assessment: measurement of insulin resistance and β-cell function in man (1985)
    Springer
    Diabetologia 28 (1985), S. 401-411 
    Details
    ISSN: 1432-0428
    Keywords: Insulin resistance ; β-cell function ; mathematical model ; glucose infusion ; Type 2 diabetes ; plasma insulin ; plasma glucose
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Continuous infusion of glucose with model assessment (CIGMA) is a new method of assessing glucose tolerance, insulin resistance and β-cell function. It consists of a continuous glucose infusion 5 mg glucose/kg ideal body weight per min for 60 min, with measurement of plasma glucose and insulin concentrations. These are similar to postprandial levels, change slowly, and depend on the dynamic interaction between the insulin produced and its effect on glucose turnover. The concentrations can be interpreted using a mathematical model of glucose and insulin homeostasis to assess insulin resistance and β-cell function. In 23 subjects (12 normal and 11 with Type 2 (non-insulin-dependent diabetes) the insulin resistance measured by CIGMA correlated with that measured independently by euglycaemic clamp (Rs = 0.87, p 〈 0.0001). With normal insulin resistance defined as 1, the median resistance in normal subjects was 1.35 by CIGMA and 1.39 by clamp, and in diabetic patients 4.0 by CIGMA and 3.96 by clamp. In 21 subjects (10 normal and 11 Type 2 diabetic) the β-cell function measured by CIGMA correlated with steady-state plasma insulin levels during hyperglycaemic clamp at 10 mmol/l (Rs=0.64, p 〈 0.002). The CIGMA coefficient of variability was 21% for resistance and 19% for β-cell function. CIGMA is a simple, non-labour-intensive method for assessing insulin resistance and β-cell function in normal and Type 2 diabetic subjects who do not have glycosuria during the test.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00280882
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  • 7
    Electronic Resource
    Electronic Resource
    Homeostasis model assessment: insulin resistance and β-cell function from fasting plasma glucose and insulin concentrations in man (1985)
    Springer
    Diabetologia 28 (1985), S. 412-419 
    Details
    ISSN: 1432-0428
    Keywords: β-cell function ; insulin resistance ; mathematical model ; intravenous glucose tolerance test ; glucose clamp ; insulin receptors ; Type 2 diabetes ; insulin ; glucose
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The steady-state basal plasma glucose and insulin concentrations are determined by their interaction in a feedback loop. A computer-solved model has been used to predict the homeostatic concentrations which arise from varying degrees of β-cell deficiency and insulin resistance. Comparison of a patient's fasting values with the model's predictions allows a quantitative assessment of the contributions of insulin resistance and deficient β-cell function to the fasting hyperglycaemia (homeostasis model assessment, HOMA). The accuracy and precision of the estimate have been determined by comparison with independent measures of insulin resistance and β-cell function using hyperglycaemic and euglycaemic clamps and an intravenous glucose tolerance test. The estimate of insulin resistance obtained by homeostasis model assessment correlated with estimates obtained by use of the euglycaemic clamp (Rs = 0.88, p 〈 0.0001), the fasting insulin concentration (Rs = 0.81, p 〈 0.0001), and the hyperglycaemic clamp, (Rs = 0.69, p 〈 0.01). There was no correlation with any aspect of insulin-receptor binding. The estimate of deficient β-cell function obtained by homeostasis model assessment correlated with that derived using the hyperglycaemic clamp (Rs = 0.61, p 〈 0.01) and with the estimate from the intravenous glucose tolerance test (Rs = 0.64, p 〈 0.05). The low precision of the estimates from the model (coefficients of variation: 31% for insulin resistance and 32% for β-cell deficit) limits its use, but the correlation of the model's estimates with patient data accords with the hypothesis that basal glucose and insulin interactions are largely determined by a simple feed back loop.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00280883
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