Radioimmunoassay of Gastric Inhibitory Polypeptide

Morris, Brian

doi:10.1177/000456327801500138

Cited by 123 publications

(56 citation statements)

References 8 publications

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“…The GIP assay used has been described previously [16,17]; synthetic human GIP was used for the preparation of the standards and iodinated tracer (purified immediately prior to use by affinity chromatography) and the antiserum was raised in rabbits against natural porcine GIP; a PEG (polyethylene glycol 6000, BDH Laboratory supplies, Poole, UK)-accelerated double antibody phase separation stage was used. The detection limit of the assay was 16 pmol/l and the inter-assay CV at 300 and 497 pmol/l were 8.6 and 8.9 %, respectively.…”

Section: Methodsmentioning

confidence: 99%

The ageing entero-insular axis

et al. 1998

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Ageing is associated with a greater prevalence of impaired glucose tolerance and Type II (non-insulin-dependent) diabetes mellitus which can be associated with both a decrease in insulin secretion as well as an increase in insulin resistance [1,2].Studies in humans have shown that insulin secretion decreases with age independent of adiposity, distribution of fat and physical activity [3]. The reduction in insulin secretion in older human subjects has been attributed to decreasing responsiveness of the beta cell to glucose [4]; defects of both early and late phase insulin secretion after intravenous glucose administration have been shown in the elderly [5]. In addition, there is evidence that ageing is associated with defective intra-pancreatic processing of insulin since even those older subjects with normal glucose tolerance have been shown to have greatly increased proinsulin secretion as well as proinsulin-to-insulin molar ratios [6].Animal studies have shed further light on the impact of ageing on the biology of insulin secretion. In the rat, ageing is characterised by a high insulin content in the islet but decreased insulin secretion due primarily to impairment of beta-cell stimulus-secretion coupling which leads to greater intracellular insulin degradation secondary to failure of secretion [7]. In older mice, although islets are larger and the number of beta cells per islet is greater, the number of beta cells secreting insulin following glucose stimu- Diabetologia (1998) Summary Ageing is one of the major risk factors for glucose intolerance including impaired glucose tolerance and Type II (non-insulin-dependent) diabetes mellitus. Reduced insulin secretion has been described as part of normal ageing although there is no information on age-related changes in the secretion of the major insulinotropic hormones, glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide (7±36 amide) (GLP-1). We assessed the entero-insular axis in 6 young premenopausal and 6 older postmenopausal women following treatment with oral carbohydrate. Insulin and glucose integrated responses were similar in the younger and older groups. Total integrated responses for GIP and GLP-1 were considerably greater in the older subjects. A positive correlation between age and total integrated responses for glucose (r = 0.65; p < 0.02) as well as GLP-1 (r = 0.85; p < 0.001) was seen. We hypothesise that an age-related impairment of insulin secretion to insulinotropic hormones, GIP and GLP-1, contributes to a reduction in glucose tolerance in this age group. The pronounced compensatory increase in postprandial secretion of GIP and GLP-1 provides further evidence not only for the negative feedback relation between incretin and insulin secretion but also for the importance of the entero-insular axis in the regulation of insulin secretion.[ Diabetologia (1998)

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Section: Methodsmentioning

confidence: 99%

The ageing entero-insular axis

et al. 1998

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“…Immunoreactive GIP concentrations in plasma were measured by double-antibody radioimmunoassay [14]. This antiserum exhibited < t% cross reactivity with cholecystokinin, insulin, pancreatic polypeptide, pancreatic glucagon, porcine gut 'glucagon-like' immunoreactivity, secretin or vasoactive intestinal polypeptide.…”

Section: Methodsmentioning

confidence: 99%

Effect of co-ingestion of fat on the metabolic responses to slowly and rapidly absorbed carbohydrates

1984

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Summary. The present study examined the acute effects of coingestion of fat (37.5 g) on the post-prandial metabolic responses to 75 g of carbohydrate which was either slowly absorbed (lentils) or rapidly absorbed (potatoes). Co-ingestion of fat resulted in a significant flattening of the post-prandial glucose curves, the effect being more pronounced for the rapidly absorbed potatoes. This was probably due to delayed gastric emptying. However, the post-prandial insulin responses to either carbohydrate were not significantly reduced by fat, suggesting that the insulin response to a given glucose concentration was potentiated in the presence of fat. The gastric inhibitory polypeptide (GIP) responses to both carbohydrates were greatly increased in the presence of fat. To investigate further the possible roles of GIP in the entero-insular axis, a 5-g bolus of glucose was injected intravenously i h after lentils_ fat. This was sufficient to raise the glucose levels above the threshold reported for GIP to potentiate insulin secretion. However, despite the large differences in circulating GIP levels, the insulin response to glucose was not affected by the presence of fat. These results suggest that (1) the rate of absorption of carbohydrate is a major determinant of post-prandial metabolic responses even in the presence of fat, (2) fat-stimulated GIP secretion does not potentiate glucose-induced insulin secretion, and (3) the potentiation of the insulin response to glucose when carbohydrate is co-ingested with fat is consistent with the well-documented insulin resistance associated with high fat diets.Key words: Insulin, gastric inhibitory polypeptide, insulin sensitivity, glucose tolerance, diabetes, diet, fat, rate of carbohydrate digestion.Several studies have demonstrated the beneficial effects of high-carbohydrate, high-fibre diets in the treatment of Type 2 (non-insulin-dependent) diabetes [1,2]. The mechanism by which this dietary regimen improves long-term diabetic control remains unclear: is it due to the high complex carbohydrate, high fibre, type of fibre or low fat contents of such diets? Most previous studies have concentrated on the acute responses to complex carbohydrate and fibre components of the diet [3][4][5], and have highlighted the importance of rate of intestinal digestion and absorption in determining the metabolic responses to different carbohydrates. It has been suggested that these acute metabolic changes form the basis of long-term benefits associated with high-carbohydrate, high-fibre diets.However, as these diets are also low in fat, and insulin sensitivity has been demonstrated to be inversely related to the fat content of the diet [6,7], it is possible that * Present address: University of Melbourne, Department of Medicine, Repatriation General Hospital, Heidelberg West, Victoria, 3081, Australia the improved metabolic control is due (at least in part) to the low fat content. Thus, the aim of the present study was to examine the acute interaction of two components of the high-carbohydrate...

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“…The interassay coefficients of variation were less than 5% for these assays. Plasma and salivary insulin, C-peptide, GIP and GLP-1 were measured by in-house RIAs (Morgan et al 1978, Elliott et al 1993, Hampton & Withey 1996. The interassay coefficients of variation were less than 10% for these assays.…”

Section: Assay Proceduresmentioning

confidence: 99%

Glucose-dependent insulinotropic polypeptide and insulin-like immunoreactivity in saliva following sham-fed and swallowed meals

Messenger¹,

Clifford²,

Morgan³

2003

Journal of Endocrinology

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Gastrointestinal peptides, including insulin, glucagon and glucose-dependent insulinotropic polypeptide (GIP) have previously been reported in salivary glands. Recent evidence has suggested they might influence postprandial macronutrient metabolism. This study therefore investigated and compared postprandial hormone concentrations in saliva and plasma to determine whether their secretion was influenced by oral food stimuli. In a within-subject randomised cross-over comparison of hormone concentrations in plasma and saliva following a mixed meal, 12 subjects were given two 1708 kJ mixed meals. On one occasion the meal was chewed and swallowed (swallowed meal), on the other it was chewed and expectorated (sham-fed meal). Salivary and plasma levels of immunoreactive insulin, GIP and glucagon-like peptide-1 (GLP-1), total protein, -amylase, glucose and nonesterified fatty acid were measured before and for 90 min following the meals. Saliva total protein and -amylase rose following both meals, indicating that the stimulus for salivary protein release is related to the presence of food in the mouth. GLP-1 was not detected in saliva. Fasting salivary insulin levels were lower in saliva than plasma (28 6 vs 40 25 pmol/l respectively). Both increased following the swallowed meal but the rise in saliva was slower and less marked than in plasma (peak levels 96 18 and 270 66 pmol/l for saliva and plasma respectively, P<0·01). Both were unchanged following the sham-fed meal. GIP was detected in saliva. Fasting GIP levels were significantly higher in saliva than plasma (183 23 compared with 20 7 pmol/l, P<0·01). They decreased in saliva following both swallowed and sham-fed meals to nadirs of 117 17 and 71 12 pmol/l respectively, but rose following the swallowed meal to peak levels of 268 66 pmol/l. These findings are consistent with insulin in saliva being an ultrafiltrate of that circulating in blood, but GIP in saliva being the product of local salivary gland synthesis, whose secretion is influenced, directly or indirectly, by oral stimuli. The function of salivary GIP is unknown, but we speculate that it may play a role in the regulation of gastric acid secretion in the fasting state.

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Radioimmunoassay of Gastric Inhibitory Polypeptide

Cited by 123 publications

References 8 publications

The ageing entero-insular axis

The ageing entero-insular axis

Effect of co-ingestion of fat on the metabolic responses to slowly and rapidly absorbed carbohydrates

Glucose-dependent insulinotropic polypeptide and insulin-like immunoreactivity in saliva following sham-fed and swallowed meals

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