首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到10条相似文献,搜索用时 109 毫秒
1.
The development of a sensitive radioimmunoassay (RIA) for C-terminally amidated forms of glucagon-like peptide-1 (GLP-1) is described. Rabbits immunized with GLP-1(7–36)amide conjugated to bovine serum albumin with glutaraldehyde produced antisera containing high-affinity antibodies directed against an epitope that included the free amidated C-terminus of the peptide. These antisera could be used in a sensitive RIA (detection limit 0.1 fmol/tube) that measured GLP-1(7–36)amide and GLP-1(1–36)amide equally. Total concentrations of amidated GLP-1 immunoreactivity in extracts of rat hypothalamus, pancreas and intestine were determined by RIA, and resolved into GLP-1(7–36)amide, GLP-1(1–36)amide and unidentified cross-reacting substances by HPLC. Whereas only GLP-1(7–36)amide could be identified in the hypothalamus, in amounts that represented 55–94% of total glucagon-like immunoreactivity (GLI), the pancreas produced chiefly GLP-1(1–36)amide, representing 0.8–3.4% of total GLI, and only trace or undetectable amounts of GLP-1(7–36)amide (0–0.36% of total GLI). This argues against any role of intrapancreatic GLP-1(7–36)amide in the secretion of insulin. In the terminal ileum total amidated GLP-1 immunoreactivity represented 27–73% of total GLI, and in five of six specimens only GLP-1(7–36)amide could be identified on HPLC, in amounts representing 13–17% of total GLI. Only one specimen of terminal ileum contained HPLC-identified GLP-1(1–36)amide (13% of total GLI) in addition to GLP-1(7–36)amide (31% of total GLI). Acid–ethanol extraction of peptide-free rat plasma with added GLP-1(7–36)amide gave recoveries of 91±SEM 2% in the range 20–200 pmol/l. Basal plasma amidated GLP-1 in six unanaesthetized rats was 4.1±1.1 pmol/l and rose to a maximum of 15.4±3.0 pmol/l 10 min after intragastric glucose 1 g/kg, illustrating the modest level of plasma responses of amidated forms of GLP-1.  相似文献   

2.
The effects of glucagon-like peptide 1 (7-36) amide [GLP-1 (7-36) amide] and glucagon on the release of islet amyloid polypeptide (IAPP), or amylin, from the isolated perfused rat pancreas were studied. In the presence of 5.6 mM glucose, GLP-1 (7-36) amide and glucagon stimulated the release of amylin from the perfused pancreas. The infusion of GLP-1 (7-36) amide at a concentration of 10(-9) M elicited a biphasic release of amylin similar to that of insulin. The cumulative output of amylin induced by 10(-9)M GLP-1 (7-36) amide was significantly higher than that by 10(-9)M glucagon (p less than 0.01). The amylin/insulin molar ratios induced by GLP-1 (7-36) amide and glucagon were about 1% and did not differ significantly. These findings suggest that GLP-1 (7-36) amide and glucagon stimulate the release of amylin from the pancreas and that the concomitant secretion of amylin and insulin might contribute to glucose homeostasis.  相似文献   

3.
We previously reported that GLP-1(7-36)amide had glucagonostatic action as well as insulinotropic action in the perfused rat pancreas. In this study, we examined the effect of GLP-1(7-36)amide on glucagon secretion and cAMP concentration in glucagon-secreting cell line, In-R1-G9. GLP-1(7-36)amide (1nM) significantly suppressed glucagon secretion and decreased cAMP concentration in the cells. GLP-1(1-37) did not affect glucagon secretion. It is suggested that inhibitory effect of GLP-1(7-36)amide on glucagon secretion is at least partly mediated by adenylate cyclase system.  相似文献   

4.
The priming effect of glucagon-like peptide-1 (7-36) amide (GLP-1 (7-36) amide), glucose-dependent insulin-releasing polypeptide (GIP) and cholecystokinin-8 (CCK-8) on glucose-induced insulin secretion from rat pancreas was investigated. The isolated pancreas was perfused in vitro with Krebs-Ringer bicarbonate buffer containing 2.8 mmol/l glucose. After 10 min this medium was supplemented with GLP-1 (7-36) amide, GIP or CCK-8 (10, 100, 1000 pmol/l) for 10 min. After an additional 10 min period with 2.8 mmol/l glucose alone, insulin secretion was stimulated with buffer containing 10 mmol/l glucose for 44 min. In control experiments the typical biphasic insulin response to 10 mmol/l glucose occurred. Pretreatment of the pancreas with GIP augmented insulin secretion: 10 pmol/l GIP enhanced only the first phase of the secretory response to 10 mmol/l glucose; 100 and 1000 pmol/l GIP stimulated both phases of hormone secretion. After exposure to CCK-8, enhanced insulin release during the first (at 10 and 1000 pmol/l CCK-8) and the second phase (at 1000 pmol/l) was observed. Priming with 100 pmol/l GLP-1 (7-36) amide significantly amplified the first and 1000 pmol/l GLP-1 (7-36) amide both secretion periods, 10 pmol/l GLP-1 (7-36) amide had no significant effect. All three peptide hormones influenced the first, quickly arising secretory response more than the second phase. Priming with forskolin (30 mM) enhanced the secretory response to 10 mM glucose plus 0.5 nM GLP-1 (7-36) amide 4-fold. With a glucose-responsive B-cell line (HIT cells), we investigated the hypothesis that the priming effect of GLP-1 (7-36) amide is mediated by the adenylate cyclase system. Priming with either IBMX (0.1 mM) or forskolin (2.5 microM) enhanced the insulin release after a consecutive glucose stimulation (5 mM). This effect was pronounced when GLP-1 (7-36) amide (100 pM) was added during glucose stimulation. Priming capacities of intestinal peptide hormones may be involved in the regulation of postprandial insulin release. The incretin action of these hormones can probably, at least in part, be explained by these effects. The priming effect of GLP-1 (7-36) amide is most likely mediated by the adenylate cyclase system.  相似文献   

5.
Glucagon-like peptide 1 (7-36) amide (GLP-1) and exendin-4 are gastrointestinal hormones as well as neuropeptides involved in glucose homeostasis and feeding regulation, both peripherally and at the central nervous system (CNS), acting through the same GLP-1 receptor. Aminergic neurotransmitters play a role in the modulation of feeding in the hypothalamus and we have previously found that peripheral hormones and neuropeptides, which are known to modulate feeding in the central nervous system, are able to modify catecholamine and serotonin release in the hypothalamus. In the present paper we have evaluated the effects of GLP-1 and exendin-4 on dopamine, norepinephrine, and serotonin release from rat hypothalamic synaptosomes, in vitro. We found that glucagon-like peptide 1 (7-36) amide and exendin-4 did not modify either basal or depolarization-induced dopamine and norepinephrine release; on the other hand glucagon-like peptide 1 (7-36) amide and exendin-4 stimulated serotonin release, in a dose dependent manner. We can conclude that the central anorectic effects of GLP-1 agonists could be partially mediated by increased serotonin release in the hypothalamus, leaving the catecholamine release unaffected.  相似文献   

6.
Glucagon-like peptide-1 (GLP-1) was purified to homogeneity by HPLC and anion-exchange chromatography. A molecular mass of 3297.4 Da was obtained by FAB mass spectrometry which corresponded exactly to GLP-1 7-36 NH2, providing evidence that amidation occurs at an arginine residue during the post-translational processing of GLP-1. The distribution of GLP-1 7-36 NH2-like immunoreactivity (GLP-1 7-36 NH2 IR) was determined in the rat gastrointestinal tract. Highest concentrations were found in terminal ileum and colon. Streptozocin-induced diabetic rats, who showed a significant increase in food intake, had a significant increase of GLP-1 7-36 NH2 IR in the colon.  相似文献   

7.
Abstract: Specific binding of glucagon-like peptide (GLP)-1(7–36)amide was detected in several rat brain areas, with the highest values being found in hypothalamic nuclei and the nucleus of the solitary tract. In hypothalamus and brainstem homogenate binding of 125I-GLP-1(7–36)amide was time, temperature, and protein content dependent and was inhibited by unlabeled proglucagon-derived peptides. The rank order of potency was GLP-1(7–36)amide ? GLP-1(1–36)amide > GLP-1(1–37) ? GLP-2 > glucagon. Scatchard analysis of the steady-state binding data was consistent with the presence of both high- and low-affinity binding sites in hypothalamus and brainstem. Brain 125I-GLP-1(7–36)amide-binding protein complexes were covalently cross-linked using disuccinimidyl suberate and analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. A single radiolabeled band of Mr 56,000 identified in both hypothalamus and brainstem homogenates was unaffected by reducing agents. An excess of unlabeled GLP-1(7–36)amide abolished the band labeling, whereas glucagon had no effect. Other unlabeled GLPs inhibited Mr 56,000 complex labeling with the following order of potency: GLP-1(1–36)amide > GLP-1(1–37) > GLP-2. The binding of 125I-GLP-1(7–36)amide and the intensity of the cross-linked band were similarly inhibited in a dose-response manner by increasing concentrations of unlabeled GLP-1(7–36)amide. Covalent Mr 56,000 125I-GLP-1(7–36)amide-binding protein complexes solubilized by Triton X-100 were adsorbed onto wheat germ agglutinin. Our results suggest that the GLP-1(7–36)amide receptor in rat brain is a glycoprotein with a single binding subunit that has a greater molecular weight but binding features and ligand specificity similar to those of its peripheral tissue counterparts.  相似文献   

8.
Glucagon-like peptide 1 (GLP-1) lowers glycemia by modulating gastric emptying and endocrine pancreatic secretion. Rapidly after its secretion, GLP-1-(7-36) amide is degraded to the metabolite GLP-1-(9-36) amide. The effects of GLP-1-(9-36) amide in humans are less well characterized. Fourteen healthy volunteers were studied with intravenous infusion of GLP-1-(7-36) amide, GLP-1-(9-36) amide, or placebo over 390 min. After 30 min, a solid test meal was served, and gastric emptying was assessed. Blood was drawn for GLP-1 (total and intact), glucose, insulin, C-peptide, and glucagon measurements. Administration of GLP-1-(7-36) amide and GLP-1-(9-36) amide significantly raised total GLP-1 plasma levels. Plasma concentrations of intact GLP-1 increased to 21 +/- 5 pmol/l during the infusion of GLP-1-(7-36) amide but remained unchanged during GLP-1-(9-36) amide infusion [5 +/- 3 pmol/l; P < 0.001 vs. GLP-1-(7-36) amide administration]. GLP-1-(7-36) amide reduced fasting and postprandial glucose concentrations (P < 0.001) and delayed gastric emptying (P < 0.001). The GLP-1 metabolite had no influence on insulin or C-peptide concentrations. Glucagon levels were lowered by GLP-1-(7-36) amide but not by GLP-1-(9-36) amide. However, the postprandial rise in glycemia was reduced significantly (by approximately 6 mg/dl) by GLP-1-(9-36) amide (P < 0.05). In contrast, gastric emptying was completely unaffected by the GLP-1 metabolite. The GLP-1 metabolite lowers postprandial glycemia independently of changes in insulin and glucagon secretion or in the rate of gastric emptying. Most likely, this is because of direct effects on glucose disposal. However, the glucose-lowering potential of GLP-1-(9-36) amide appears to be small compared with that of intact GLP-1-(7-36) amide.  相似文献   

9.
High-affinity binding sites for glucagon-like peptide-1 7-36 amide (GLP-1 7-36 NH2) were identified in rat brain and lung membranes. Binding of [125I]GLP-1 7-36 NH2 was rapid, reversible, specific, saturable and pH dependent. Specific binding in the central nervous system was particularly high in the hypothalamus and the brain stem. Oxyntomodulin, glucagon-like peptide-1, glucagon-like peptide-2 and glucagon were 100-1000-fold less potent than GLP-1 7-36 NH2 in competition for this binding site.  相似文献   

10.
In the present work, several experimental approaches were used to determine the presence of the glucagon-like peptide-1 receptor (GLP-1R) and the biological actions of its ligand in the human brain. In situ hybridization histochemistry revealed specific labelling for GLP-1 receptor mRNA in several brain areas. In addition, GLP-1R, glucose transporter isoform (GLUT-2) and glucokinase (GK) mRNAs were identified in the same cells, especially in areas of the hypothalamus involved in feeding behaviour. GLP-1R gene expression in the human brain gave rise to a protein of 56 kDa as determined by affinity cross-linking assays. Specific binding of 125I-GLP-1(7-36) amide to the GLP-1R was detected in several brain areas and was inhibited by unlabelled GLP-1(7-36) amide, exendin-4 and exendin (9-39). A further aim of this work was to evaluate cerebral-glucose metabolism in control subjects by positron emission tomography (PET), using 2-[F-18] deoxy-D-glucose (FDG). Statistical analysis of the PET studies revealed that the administration of GLP-1(7-36) amide significantly reduced (p < 0.001) cerebral glucose metabolism in hypothalamus and brainstem. Because FDG-6-phosphate is not a substrate for subsequent metabolic reactions, the lower activity observed in these areas after peptide administration may be due to reduction of the glucose transport and/or glucose phosphorylation, which should modulate the glucose sensing process in the GLUT-2- and GK-containing cells.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号