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Ashley I Taylor, Nigel Irwin, Aine M McKillop, Steven Patterson, Peter R Flatt and Victor A Gault

has examined the plasma stability and satiety effects of xenin, and further characterised the glucose-lowering and insulinotropic effects of xenin both alongside GIP, glucagon-like peptide-1 (GLP1) and neurotensin. Materials and Methods Degradation of

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Jung-Hoon Kang, Seo-Yoon Chang, Hyun-Jong Jang, Dong-Bin Kim, Gyeong Ryul Ryu, Seung Hyun Ko, In-Kyung Jeong, Yang-Hyeok Jo and Myung-Jun Kim

or reduce iNOS expression may be necessary for the prevention or inhibition of β-cell damage. Glucagon-like peptide-1 (GLP-1) and its potent agonist exendin-4 (EX-4) have received great attention because of their insulinotropic and β

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U Ritzel, U Leonhardt, M Ottleben, A Ruhmann, K Eckart, J Spiess and G Ramadori

Glucagon-like peptide-1 (GLP-1) is the most potent endogenous insulin-stimulating hormone. In the present study the plasma stability and biological activity of a GLP-1 analog, [Ser]GLP-1(7-36)amide, in which the second N-terminal amino acid alanine was replaced by serine, was evaluated in vitro and in vivo. Incubation of GLP-1 with human or rat plasma resulted in degradation of native GLP-1(7-36)amide to GLP-1(9-36)amide, while [Ser]GLP-1(7-36)amide was not significantly degraded by plasma enzymes. Using glucose-responsive HIT-T15 cells, [Ser]GLP-1(7-36)amide showed strong insulinotropic activity, which was inhibited by the specific GLP-1 receptor antagonist exendin-4(9-39)amide. Simultaneous i.v. injection of [Ser]GLP-1(7-36)amide and glucose in rats induced a twofold higher increase in plasma insulin levels than unmodified GLP-1(7-36)amide with glucose and a fivefold higher increase than glucose alone. [Ser]GLP-1(7-36)amide induced a 1.5-fold higher increase in plasma insulin than GLP-1(7-36)amide when given 1 h before i.v. application of glucose. The insulinotropic effect of [Ser]GLP-1(7-36)amide was suppressed by i.v. application of exendin-4(9-39)amide. The present data demonstrate that replacement of the second N-terminal amino acid alanine by serine improves the plasma stability of GLP-1(7-36)amide. The insulinotropic action in vitro and in vivo was not impaired significantly by this modification.

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M-J Kim, J-H Kang, Y G Park, G R Ryu, S H Ko, I-K Jeong, K-H Koh, D-J Rhie, S H Yoon, S J Hahn, M-S Kim and Y-H Jo

Introduction Glucagon-like peptide-1 (GLP-1) has been of much interest due to its β-cell-proliferating effect and role as an incretin hormone in synergizing with glucose to enhance insulin release ( Ørskov 1992 , Egan et al. 2003

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C Herrmann-Rinke, A Vöge, M Hess and B Göke

Abstract

Food ingestion induces a rapid increase in the insulinotropic glucagon-like peptide-1 (GLP-1) in plasma. Paradoxically, GLP-1 originates from the lower intestines and therefore a complex regulation of postprandial GLP-1 secretion must exist. This was addressed in the present study by utilizing an isolated vascularly perfused rat ileum preparation. Peptides and neurotransmitters thought to be candidate mediators triggering GLP-1 secretion were arterially infused and GLP-1 was measured in the venous effluent. Arterial infusion of cholinergic agonists strongly enhanced GLP-1 secretion which was counteracted by the addition of atropine. Histamine, dopamine, 5-hydoxytryptamine, γ-aminobutyric acid, and norepinephrine had no effect. Peptides of the bombesin family were strong stimulants whereas tachykinins, enkephalins, dynorphin, TRH, calcitonin-gene-related peptide and members of the secretin family, vasoactive intestinal peptide, peptide histidine isoleucine and neuropeptide Y, were less effective. The second incretin hormone, gastric inhibitory polypeptide (GIP), was the most potent stimulant of GLP-1 secretion in our study. It enhanced GLP-1 release up to sixfold above basal during the early phase followed by a sustained secretion at 400% above basal. This stimulation remained unaffected by atropine. In conclusion, in addition to luminal stimulation of nutrients, a cholinergic impulse as well as peptidergic mediators (among them possibly GIP and GRP) may have an impact on postprandial GLP-1 secretion from the rat ileum.

Journal of Endocrinology (1995) 147, 25–31

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J Schirra, P Leicht, P Hildebrand, C Beglinger, R Arnold, B Goke and M Katschinski

Twelve patients with non-insulin dependent diabetes mellitus (NIDDM) under secondary failure to sulfonylureas were studied to evaluate the effects of subcutaneous glucagon-like peptide-1(7-36)amide (GLP-1) on (a) the gastric emptying pattern of a solid meal (250 kcal) and (b) the glycemic and endocrine responses to this solid meal and an oral glucose tolerance test (OGTT, 300 kcal). 0.5 nmol/kg of GLP-1 or placebo were subcutaneously injected 20 min after meal ingestion. GLP-1 modified the pattern of gastric emptying by prolonging the time to reach maximal emptying velocity (lag period) which was followed by an acceleration in the post-lag period. The maximal emptying velocity and the emptying half-time remained unaltered. With both meals, GLP-1 diminished the postprandial glucose peak, and reduced the glycemic response during the first two postprandial hours by 54.5% (solid meal) and 32.7% (OGTT) (P < 0.05). GLP-1 markedly stimulated insulin secretion with an effect lasting for 105 min (solid meal) or 150 min (OGTT). The postprandial increase of plasma glucagon was abolished by GLP-1. GLP-1 diminished the postprandial release of pancreatic polypeptide. The initial and transient delay of gastric emptying, the enhancement of postprandial insulin release, and the inhibition of postprandial glucagon release were independent determinants (P < 0.002) of the postprandial glucose response after subcutaneous GLP-1. An inhibition of efferent vagal activity may contribute to the inhibitory effect of GLP-1 on gastric emptying.

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Sarah L Craig, Victor A Gault, Gerd Hamscher and Nigel Irwin

relates to preventing degradation and subsequent loss of bioactivity of the endogenous intestinal-derived incretin hormones, glucagon-like peptiede-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) ( Deacon 2019 ). Thus, GLP-1 and GIP

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Tianru Jin

cDNAs from these species further revealed that it encodes not only glucagon but also two glucagon-like peptide hormones, namely glucagon-like peptide-1 (GLP-1) and GLP-2 ( Lund et al . 1982 ). Glucagon is produced and released from the pancreatic α

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Y Watanabe, K Kawai, S Ohashi, C Yokota, S Suzuki and K Yamashita

Abstract

To examine the structure–activity relationships in the insulinotropic activity of glucagon-like peptide-1(7–36) amide (GLP-1(7–36)amide), we synthesized 16 analogues, including eight which were designed by amino acid substitutions at positions 10 (Ala10), 15 (Serl5), 16 (Tyr16), 17 (Arg17), 18 (Lys18), 21 (Gly21), 27 (Lys27) and 31 (Asp31) of GLP-1(7–36)amide with an amino acid of GH-releasing factor possessing only slight insulinotropic activity, and three tentative antagonists including [Glu15]-GLP-1(8–36)amide. Their insulinotropic activities were assessed by rat pancreas perfusion experiments, and binding affinity to GLP-1 receptors and stimulation of cyclic AMP (cAMP) production were evaluated using cultured RINm5F cells.

Insulinotropic activity was estimated as GLP-1(7–36)amide = Tyr16>Lys18, Lys27>Gly21>Asp31⪢Ser15,Arg17>Ala10⪢GRF>[Glu15]-GLP-1(8–36) amide. Displacement activity against 125I-labelled GLP-1 (7–36)amide binding and stimulatory activity for cAMP production in RINm5F cells correlated well with their insulinotropic activity in perfused rat pancreases.

These results demonstrate that (1) positions 10 (glycine), 15 (aspartic acid) and 17 (serine) in the amino acid sequence of GLP-1(7–36)amide, in addition to the N-terminal histidine, are essential for its insulinotropic activity through its binding to the receptor, (2) the amino acid sequences for the C-terminal half of GLP-1(7–36)amide also contribute to its binding to the receptor, although they are less important compared with those of the N-terminal half, and (3) [Glu15]-GLP-1(8–36)amide is not an antagonist of GLP-1(7–36)amide as opposed to des-His1 [Glu9]-glucagon amide which is a potent glucagon antagonist.

Journal of Endocrinology (1994) 140, 45–52

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Srividya Vasu, Mary K McGahon, R Charlotte Moffett, Tim M Curtis, J Michael Conlon, Yasser H A Abdel-Wahab and Peter R Flatt

various glucagon-like peptide-1 (GLP-1 mimetics) have been strongly promoted over the past few years ( Kahn et al. 2014 , Irwin & Flatt 2015 ). This approach has several potential advantages over development of small-molecule drugs, providing greater