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J Claustre, S Brechet, P Plaisancie, JA Chayvialle and JC Cuber

Postprandial release of peptide YY (PYY) and glucagon-like peptide-1 (GLP-1) from L cells results from both nutrient transit in the ileal lumen and neural drive of endocrine cells. The adrenosympathetic system and its effectors have been shown to induce secretion of L cells in vivo or in vitro. Because these transmitters act through three receptors, beta, alpha1, alpha2, coupled to different intracellular pathways, we evaluated the responses of L cells to specific agonists, using the model of isolated vascularly perfused rat ileum. General stimulation of adrenergic receptors with epinephrine (10(-7) M) induced significant GLP-1 and PYY secretions (94+/-38 and 257+/-59 fmol/8 min respectively) which were abolished upon propranolol (10(-7) M) pretreatment and strongly decreased upon infusion with 10(-8) M prazosin. Blockade of alpha2-receptors with idazoxan (10(-8) M) did not alter epinephrine-induced peptide secretion. The beta-adrenergic agonist isoproterenol (10(-6) M) infused for 30 min induced a transient release of GLP-1 and PYY (integrated release over the 8 min of the peak secretion: 38+/-16 and 214+/-69 fmol for GLP-1 and PYY respectively, P<0.05). Because terbutaline but not dobutamine or BRL 37,344 (10(-5) M) induced significant GLP-1 and PYY secretions (135+/-30 and 305+/-39 fmol/8 min respectively), isoproterenol-induced secretions are suggested to result mainly from stimulation of the beta2-isoreceptor type. In contrast, the alpha1-agonist phenylephrine (10(-7) M) did not stimulate peptide release. When co-infused with 10(-6) M or 10(-7) M isoproterenol, 10(-7) M phenylephrine raised GLP-1 release to 174+/-53 and 108+/-28 fmol/8 min respectively (vs 38+/-16 and 35+/-10 fmol/8 min for isoproterenol alone, P<0.05) whereas PYY secretion was not significantly increased. Clonidine (10(-7) M), an alpha2-agonist, induced a moderate and delayed increase of GLP-1 and PYY but abolished the isoproterenol-induced peptide secretion. Our results showed that general stimulation of adrenergic receptors stimulates the secretory activity of ileal endocrine L cells. The net peptide secretion results from the activation of the beta2-isoreceptor type. Additionally, GLP-1 and PYY secretions are positively modulated by alpha1-receptor stimulation and inhibited by alpha2-receptor activation upon beta-receptor occupation.

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G. Richter, R. Göke, B. Göke and R. Arnold

ABSTRACT

The effect of dexamethasone on binding of glucagonlike peptide-1(7–36)amide (GLP-1(7–36)amide) to rat insulinoma-derived cells (RINm5F) was investigated. Preincubation of RINm5F cells with dexamethasone (100 nmol/l) for 24 h resulted in a decrease of GLP1(7-36)amide binding to 55·0±8·16% (mean ± s.e.m.), incubation for 48 h to 39·1±1·76%, and for 72 h to 15·5±4·35% of maximal binding. The GLP-1(7–36)amide-induced stimulation of cyclic AMP (cAMP) production was significantly decreased to 61·03±7·4% of maximum production in cells pretreated with dexamethasone (100 nmol/l) for 48 h. The decreased binding was due to a reduction of the receptor number while the receptor affinity remained unchanged. These inhibitory effects on binding and cAMP formation induced by dexamethasone were completely abolished when the antiglucocorticoid RU 38486 (100 nmol/l) was added during preincubation with dexamethasone. RU 38486 alone had no effects. Our data suggest that the biological action of GLP-1(7–36) amide at the B-cell may be modified by glucocorticoids.

Journal of Endocrinology (1990) 126, 445–450

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EG Siegel, A Seidenstucker, B Gallwitz, F Schmitz, A Reinecke-Luthge, G Kloppel, UR Folsch and WE Schmidt

Liver cirrhosis is often accompanied by a disturbed carbohydrate metabolism similar to type 2 diabetes. To investigate the severity of the defect in insulin secretion in this form of diabetes, we measured insulin release from isolated pancreatic islets of rats with CCl(4)-phenobarbital-induced liver cirrhosis. Cirrhosis was confirmed by clinical signs, elevated liver enzymes and histology. Fasting venous plasma glucose concentrations were equal in rats with liver cirrhosis and in controls. Plasma insulin and glucagon concentrations were significantly greater (P<0.01) in cirrhotic rats than in control animals. Glucose (16.7 mM)-induced stimulation of insulin release from pancreatic islets revealed a twofold increase in control and cirrhotic rats. Basal and stimulated insulin secretion, however, were significantly lower in cirrhotic animals. The incretin hormone, glucagon-like peptide-1 (GLP-1), has therapeutic potential for the treatment of type 2 diabetes. Therefore, islets from control and cirrhotic animals were incubated with GLP-1 in concentrations from 10(-)(11) to 10(-)(6) M. GLP-1 stimulated insulin release in a concentration-dependent manner. In islets from cirrhotic rats, basal and stimulated insulin secretion was blunted compared with controls. These data show that the hyperinsulinemia observed in liver cirrhosis is not due to an increase of insulin secretion from islets, but could be explained by decreased hepatic clearance of insulin. GLP-1 may ameliorate diabetes in patients with liver cirrhosis.

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R. M. Elliott, L. M. Morgan, J. A. Tredger, S. Deacon, J. Wright and V. Marks

ABSTRACT

The acute effects of different macronutrients on the secretion of glucagon-like peptide-1(7–36)amide (GLP-1(7–36)amide) and glucose-dependent insulinotropic polypeptide (GIP) were compared in healthy human subjects. Circulating levels of the two hormones were measured over a 24-h period during which subjects consumed a mixed diet. In the first study, eight subjects consumed three equicaloric (375 kcal) test meals of carbohydrate, fat and protein. Small increases in plasma GLP-1(7–36) amide were found after all meals. Levels reached a maximum 30 min after the carbohydrate and 150 min after the fat load. Ingestion of both carbohydrate and fat induced substantial rises in GIP secretion, but the protein meal had no effect. In a second study, eight subjects consumed 75 g glucose or the equivalent portion of complex carbohydrate as boiled brown rice or barley. Plasma GIP, insulin and glucose levels increased after all three meals, the largest increase being observed following glucose and the smallest following the barley meal. Plasma GLP-1(7–36)amide levels rose only following the glucose meal. In the 24-h study, plasma GLP-1(7–36)amide and GIP concentrations were increased following every meal and remained elevated throughout the day, only falling to fasting levels at night. The increases in circulating GLP-1(7–36)amide and GIP levels following carbohydrate or a mixed meal are consistent with their role as incretins. The more sustained rises observed in the daytime during the 24-h study are consistent with an anabolic role in lipid metabolism.

Journal of Endocrinology (1993) 138, 159–166

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T. P. Mommsen and T. W. Moon

ABSTRACT

Salmon glucagon-like peptide (GLP), bovine glucagon (B-glucagon) and anglerfish glucagon (AF-glucagon), all activate glucose production in teleost hepatocytes through gluconeogenesis and glycogenolysis, but notable species differences exist in their respective effectiveness. In trout hepatocytes, gluconeogenesis appears to be the main target of hormone action. In eel cells, sampled in November, glycogenolysis was activated threefold, while gluconeogenesis was increased by 12% only. In March, glycogenolytic activation was 1·7-fold, while gluconeogenesis was increased by about 1·7-fold after exposure to B-glucagon. In brown bullhead cells, increases in glycogenolysis from seven- (GLP) to tenfold (B- and AF-glucagon) were noted, while activation of gluconeogenesis was slight. Fragments of two AF-glucagons (19–29) revealed only insignificant metabolic activity. Treatment of eel cells with B-glucagon led to large (up to 20-fold) increases in intracellular cyclic AMP (cAMP) concentrations, while exposure to GLP was accompanied by a modest (< twofold) increase in cAMP, although metabolic effectiveness (gluconeogenesis and glycogenolysis) was similar for the two treatments. Under identical conditions, brown bullhead cellular cAMP responded poorly. Levels of cAMP peaked within 15 min following hormone application. The results imply that no simple or direct relationship exists between the amount of intracellular cAMP and the metabolic action of the glucagon family of hormones. It can further be concluded that GLPs are important regulators of hepatic metabolism, influencing identical targets as glucagon, while the mechanisms of action seem to differ.

Journal of Endocrinology (1990) 126, 109–118

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JM Conlon, JB Kim, A Johansson and S Kikuyama

Electrospray mass spectrometry coupled with reverse-phase HPLC was used to identify peptides in the molecular mass range 3000-6000 Da in extracts of the pancreata of the clawed frog Xenopus laevis (Anura: Pipidae) and the red-bellied newt Cynops pyrrhogaster (Caudata: Salamandridae). Amino acid sequences of insulins, peptides derived from the post-translational processing of proglucagons and pancreatic polypeptide were determined by automated Edman degradation. Three molecular forms of insulin were isolated from the tetraploid organism X. laevis that represent insulin-1 and insulin-2, as deduced from the nucleotide sequences of previously characterized cDNAs, and a third form which differed from insulin-2 by the single amino acid substitution Asp(21)-->Glu in the B-chain. The amino acid sequence of Xenopus preproglucagons (genes 1 and 2 ) may be deduced from the nucleotide sequences of cDNAs but the pathways of post-translation processing of the precursors are not known. Two molecular forms of glucagon with 36 amino acids, derived from genes 1 and 2 and representing glucagon-29 extended from its C terminus by different heptapeptides, and five molecular forms of glucagon-like peptide 1 (GLP-1) were isolated. The GLPs represent proglucagon-(77-113), -(122-158) and -(160-191) from gene 1, and proglucagon-(77-113) and -(160-191) from gene 2. A single molecular form of insulin, glucagon-36, a C-terminally alpha-amidated GLP-1 with 30 amino acid residues, a 33 amino acid residue GLP-2 and pancreatic polypeptide were isolated from the pancreatic extract of the diploid organism C. pyrrhogaster. This study has illustrated the power of electrospray mass spectrometry for the rapid and reliable identification of peptides in chromatographic fractions without the need to use radioimmunoassay, radioreceptor assay or bioassay.

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L Friis-Hansen, KA Lacourse, LC Samuelson and JJ Holst

The maturation of many peptide hormones is attenuated in carboxypeptidase E (CPE)-deficient fat/fat mice, leading to a slowly developing, adult-onset obesity with mild diabetes. To determine the contribution of the hormones generated from the proglucagon precursor to this phenotype, we studied the tissue-specific processing of glucagon and glucagon-like peptide-1 (GLP-1) in these mice. In all tissues examined there was a great reduction in mature amidated GLP-1. Furthermore, a lack of CPE attenuates prohormone convertase processing of proglucagon in both the pancreas and the intestine. These findings suggest that defects in proglucagon processing together with other endocrine malfunctions could contribute to the diabetic and obesity phenotype in fat/fat mice.

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S M Hampton, L M Morgan, N Lawrence, T Anastasiadou, F Norris, S Deacon, D Ribeiro and J Arendt

Abstract

This study was designed to investigate postprandial responses to a mixed meal in simulated shift work conditions. Nine normal healthy subjects (six males and three females) were studied on two occasions at the same clock time (1330 h) after consuming test meals, first in their normal environment and secondly after a 9 h phase advance (body clock time 2230 h). Plasma glucose, insulin, glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide-1 (GLP-1), triacylglycerol (TAG) and non-esterified fatty acids (NEFAs) were determined at intervals for 6 h after each test meal. Postprandial plasma glucose, insulin, GIP and GLP-1 profiles were evaluated by calculating areas under the curve (AUC) for the first 2 h and the last 4 h of the sampling together with total AUC. Significantly higher postprandial glucose responses (total AUC) were observed after the phase shift than before (AUC 0–360 min, 2·01 (1·51–2·19) vs 1·79 (1·56–2·04) mmol/l.min; P<0·02; mean (range)). No significant difference was observed when the first 2 h of each response was compared, but significantly higher glucose levels were observed in the last 4 h of the study after the phase shift than before (AUC 120–360 min, 1·32 (1·08–1·42) vs 1·16 (1·00–1·28) mmol/l.min; P<0·05). Similar results were obtained for insulin (AUC 0—360 min, 81·72 (30·75– 124·97) vs 58·98 (28·03–92·57) pmol/l.min; P<0·01; AUC 120–360 min, 40·73 (16·20–65·25) vs 25·71 (14·25–37·33) pmol/l.min; P<0·02). No differences were observed in postprandial plasma GIP and GLP-1 responses before and after the phase shift. Postprandial circulating lipid levels were affected by phase shifting. Peak plasma TAG levels occurred 5 h postprandially before the phase shift. Postprandial rises in plasma TAG were significantly delayed after the phase shift and TAG levels continued to rise throughout the study. Plasma postprandial NEFA levels fell during the first 3 h both before and after the phase shift. Their rate of return to basal levels was significantly delayed after the phase shift compared with before. This study demonstrates that a simulated phase shift can significantly alter pancreatic B-cell responses and postprandial glucose and lipid metabolism.

Journal of Endocrinology (1996) 151, 259–267

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L Morgan, J Arendt, D Owens, S Folkard, S Hampton, S Deacon, J English, D Ribeiro and K Taylor

This study was undertaken to determine whether the internal clock contributes to the hormone and metabolic responses following food, in an experiment designed to dissociate internal clock effects from other factors. Nine female subjects participated. They lived indoors for 31 days with normal time cues, including the natural light: darkness cycle. For 7 days they retired to bed from 0000 h to 0800 h. They then underwent a 26-h 'constant routine' (CR) starting at 0800 h, being seated awake in dim light with hourly 88 Kcal drinks. They then lived on an imposed 27-h day (18 h of wakefulness, 9 h allowed for sleep), for a total of 27 days. A second 26-h CR, starting at 2200 h, was completed. During each CR salivary melatonin and plasma glucose, triacylglycerol (TAG), non-essential fatty acids (NEFA), insulin, gastric inhibitory peptide (GIP) and glucagon-like peptide-1 (GLP-1) were measured hourly. Melatonin and body temperature data indicated no shift in the endogenous clock during the 27-h imposed schedule. Postprandial NEFA, GIP and GLP-1 showed no consistent effects. Glucose, TAG and insulin increased during the night in the first CR. There was a significant effect of both the endogenous clock and sleep for glucose and TAG, but not for insulin. These findings may be relevant to the known increased risk of cardiovascular disease amongst shift workers.

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Antonella Amato, Sara Baldassano and Flavia Mulè

the gastrointestinal tract and in the brain, resulting in glucagon-like peptide-1 (GLP1), GLP2, intervening peptide-2, oxynthomodulin and glicentin ( Ugleholdt et al . 2004 ). The studies on proglucagon-derived peptides have supplied two classes of