Efficacy and safety of high-dose glucagon-like peptide-1, glucagon-like peptide-1/glucose-dependent insulinotropic peptide,and glucagon-like peptide-1/glucagon receptor agonists in type 2 diabetes

Glucagon-like peptide-1 receptor agonists (GLP-1 RAs) have become agents of choice for people with type 2 diabetes (T2D) with established cardiovascular disease or in high-risk individuals. With currently available GLP-1 RAs, 51%-79% of subjects achieve an HbA1c target of less than 7.0% and 4%-27% lose 10% of body weight, illustrating the need for more potent agents. Three databases (PubMed, Cochrane, Web of Science) were searched using the MESH terms ‘glucagon-like peptide-1 receptor agonist’, ‘glucagon receptor agonist’, ‘glucose-dependent insulinotropic peptide’, ‘dual or co-agonist’, and ‘tirzepatide’. Quality of papers was scored using PRISMA guidelines. Risk of bias was evaluated using the Cochrane assessment tool. An HbA1c target of less than 7.0% was attained by up to 80% with high-dose GLP-1 RAs and up to 97% with tirzepatide, with even up to 62% of people with T2D reaching an HbA1c of less than 5.7%. A body weight loss of 10% or greater was obtained by up to 50% and up to 69% with high-dose GLP-1 RAs or tirzepatide, respectively. The glucose- and weight-lowering effects of the GLP-1/glucagon RA cotadutide equal those of liraglutide 1.8 mg. Gastrointestinal side effects of high-dose GLP-1 RAs and co-agonists occurred in 30%-70% of patients, mostly arising within the first 2 weeks of the first dose, being mild or moderate in severity, and transient. The development of high-dose GLP-1 RAs and the dual GLP-1/glucose-dependent insulinotropic peptide RA tirzepatide resulted in increasing numbers of people reaching HbA1c and body weight targets, with up to 62% attaining normoglycaemia with 15-mg tirzepatide. Whether this will also translate to better cardiovascular outcomes and affect treatment guidelines remains to be studied.     

2型糖尿病胃转流术后胰高血糖素样肽-1的变化及其意义

目的 探讨2型糖尿病患者行胃转流术后血清胰高血糖素样肽-1 （GLP-1）的变化及意义.方法 对37例2型糖尿病患者行胃转流术,手术前后检测空腹血糖（FPG）、餐后2h血糖（2 h PG）、糖化血红蛋白（HbA1c）、空腹胰高血糖素样肽-1（FGLP-1）、餐后2h胰高血糖素样肽-1（2 h GLP-1）,并计算胰岛素敏感指数（（ISI）=1/FPG×FIns.结果 37例患者均获随访1年以上,29例达到完全缓解,5例部分缓解,3例无效,总有效率为91.9％.与术前比较,术后FPG、2 h PG、及HbA1c呈显著下降,FGLP-1、2 h GLP-1及ISI则较术前明显升高（P均＜0.05）;FGLP-1、2 h GLP-1与ISI呈正相关（r分别为0.64、0.58,P＜0.01或＜0.05）.结论 胃转流术治疗2型糖尿病有明显效果,其作用机制之一是术后患者肠源性GLP-1的分泌增加进而改善胰岛素敏感性.     

PEGylated glucagon-like peptide-1 displays preserved effects on insulin release in isolated pancreatic islets and improved biological activity in db/db mice

Aims/hypothesis The rapid degradation and clearance of glucagon-like peptide-1 (GLP-1) by the enzymes dipeptidyl peptidase-IV and neutral endopeptidase 24.11 are the main impediments to the development of GLP-1 as a potential glucose-lowering agent. In this study, new enzyme-resistant polyethylene glycol (PEG)-conjugated GLP-1 analogues were designed and examined for metabolic stability and biological potency.Materials and methods Two mono-PEGylated GLP-1 analogues, N-terminally modified N-PEG/GLP-1 and Lys-modified Lys-PEG/GLP-1, were prepared. Stability was tested in plasma and tissue extracts. In vitro insulin release studies were performed using isolated rat pancreatic islets, while in vivo glycaemic responses were measured in db/db mice.Results The half-life of Lys-PEG/GLP-1 was 40-, 10- and 28-fold longer than that of GLP-1 in plasma, liver and kidney homogenates, respectively. Lys-PEG/GLP-1 stimulated insulin secretion in the islets in a dose- and glucose-dependent manner, and was as potent as GLP-1. In contrast, N-PEG/GLP-1 showed extended metabolic stability but had significantly lower biological activity. The administration of Lys-PEG/GLP-1 (9 nmol/kg i.p.) to non-fasted db/db mice stabilised glycaemia (p<0.001), whereas GLP-1 (9 nmol/kg) only caused small changes in glucose level. During OGTT in fasted db/db mice, Lys-PEG/GLP-1 administered at 1, 3 and 9 nmol/kg (i.p.) reduced the glucose AUC_0–3h by 48.7±9.4, 55.0±2.9 and 63.4±2.5%, respectively, compared with placebo (p<0.01), whereas GLP-1 (9 nmol/kg) lowered the glucose level by 39.5±12.9% (p<0.01).Conclusions/interpretation This study demonstrates that site-specific PEGylated GLP-1 analogues are resistant to degradation. The enhanced biological potencies of these analogues highlight their potential as new, GLP-1-like glucose-lowering agents.     

Antidiabetogenic action of truncated glucagon-like peptide-1 in mice

Besides its well-known stimulatory action on insulin secretion, glucagon-like peptide-1 (7-36)amide (= GLP-1) has been shown to increase the insulin-independent glucose uptake in normal individuals and the glucose elimination rate during short term conditions in diabetes. Whether such an action is evidented also in rodents and whether it persists after long-term administration are not known. This study therefore examined the influence of the peptide on glucose elimination in insulin deficient diabetic mice both acutely and following long-term administration. GLP-1 was injected intravenously (1 or 32 nmol/kg) together with glucose (2.8 mmol/kg) in both normal and alloxan-diabetic mice. It was found that the peptide at 32 nmol/kg potentiated the glucose elimination rate in both groups, i.e. also under insulin deficient conditions. In normal animals, GLP-1 also potentiated glucose-stimulated insulin secretion. In a second experimental series, GLP-1 was injected subcutaneously at 0.33 or 1.5 nmol twice daily to normal and alloxan-diabetic mice. After 5 days of treatment by the peptide at 1.5 nmol twice daily, the glucose elimination rate was potentiated in both groups, also when the intravenous glucose tolerance test was performed 4 h after the last injection of GLP-1. We therefore conclude that the glucose elimination is enhanced by GLP-1 in both normal and alloxan-diabetic mice, and that this effect persists after a 5 day course of subcutaneous treatment.     

Improvement in hepatic insulin sensitivity after Roux-en-Y gastric bypass in a rat model of obesity is partially mediated via hypothalamic insulin action

Aims/hypothesis

Roux-en-Y gastric bypass (RYGB) surgery, an effective treatment for morbid obesity, commonly leads to near complete resolution of type 2 diabetes. The underlying mechanisms, however, remain unclear and factors other than weight loss alone may be involved.

Methods

To determine whether increased hypothalamic insulin sensitivity after RYGB drives the rapid improvement in glucose metabolism, high-fat-fed rats received either an insulin receptor (IR) antisense vector or a control lentiviral vector that was microinjected into the ventromedial hypothalamus (VMH). Six weeks later, rats underwent RYGB or control gastrointestinal surgery.

Results

Four weeks after surgery, weight loss was comparable in RYGB and surgical controls. Nevertheless, only RYGB rats that received the control vector demonstrated both improved hepatic and peripheral insulin sensitivity. Insulin suppressed hepatic glucose production (HGP) by 50% (p?<?0.05) with RYGB, whereas the effect of insulin on HGP was completely absent in VMH IR knockdown (IRkd) rats. By contrast, both RYGB groups displayed an identical twofold increase in insulin-stimulated peripheral glucose uptake. The animals that underwent control gastrointestinal surgery failed to show any improvement in either hepatic or peripheral insulin sensitivity; VMH IRkd did not influence the magnitude of insulin resistance.

Conclusions/interpretation

Our findings demonstrate that RYGB surgery in high-fat-fed obese rats enhances hepatic and peripheral insulin sensitivity independently of weight loss. The improved hepatic, but not the peripheral, response to insulin is mediated centrally at the level of the VMH. These data provide direct evidence that the metabolic benefits of RYGB surgery are not simply a consequence of weight loss but likely in part involve the central nervous system.     

重组人胰高血糖素样肽1(7-36)促进INS-1细胞胰岛素释放与合成

在INS 1细胞中分别加入不同浓度的葡萄糖和重组人胰高血糖素样肽 1〔rhGLP 1(7 3 6〕溶液 ,孵育 4h ,用放免法测定上清液中胰岛素含量 ,并利用RT PCR技术对INS 1细胞的胰岛素mRNA水平作半定量分析。结果提示rhGLP 1(7 3 6)不仅能促进INS细胞的胰岛素释放 ,而且能促进胰岛素基因表达。     

Cell signalling of glucagon-like peptide-1 action in rat skeletal muscle

Glucagon-like peptide-1 (GLP-1), an incretin with glucose-dependent insulinotropic and insulin-independent antidiabetic properties, has insulin-like effects on glucose metabolism in extrapancreatic tissues participating in overall glucose homeostasis. These effects are exerted through specific receptors not associated with cAMP, an inositol phosphoglycan being a possible second messenger. In rat hepatocytes, activation of phosphatidylinositol 3-kinase (PI3K)/protein kinase B (PKB), protein kinase C (PKC) and protein phosphatase 1 (PP-1) has been shown to be involved in the GLP-1-induced stimulation of glycogen synthase. We have investigated the role of enzymes known or suggested to mediate the actions of insulin in the GLP-1-induced increase in glycogen synthase a activity in rat skeletal muscle strips. We first explored the effect of GLP-1, compared with that of insulin, on the activation of PI3K, PKB, p70s6 kinase (p70s6k) and p44/42 mitogen-activated protein kinases (MAPKs) and the action of specific inhibitors of these kinases on the insulin- and GLP-1-induced increment in glycogen synthase a activity. The study showed that GLP-1, like insulin, activated PI3K/PKB, p70s6k and p44/42. Wortmannin (a PI3K inhibitor) reduced the stimulatory action of insulin on glycogen synthase a activity and blocked that of GLP-1, rapamycin (a 70s6k inhibitor) did not affect the action of GLP-1 but abolished that of insulin, PD98059 (MAPK inhibitor) was ineffective on insulin but blocked the action of GLP-1, okadaic acid (a PP-2A inhibitor) and tumour necrosis factor-alpha (a PP-1 inhibitor) were both ineffective on GLP-1 but abolished the action of insulin, and Ro 31-8220 (an inhibitor of some PKC isoforms) reduced the effect of GLP-1 while completely preventing that of insulin. It was concluded that activation of PI3K/PKB and MAPKs is required for the GLP-1-induced increment in glycogen synthase a activity, while PKC, although apparently participating, does not seem to play an essential role; unlike in insulin signaling, p70s6k, PP-1 and PP-2A do not seem to be needed in the action of GLP-1 upon glycogen synthase a activity in rat muscle.     

Normal secretion and action of the gut incretin hormones glucagon-like peptide-1 and glucose-dependent insulinotropic polypeptide in young men with low birth weight

CONTEXT: Low birth weight (LBW) is associated with increased risk of type 2 diabetes mellitus. An impaired incretin effect was reported previously in type 2 diabetic patients. OBJECTIVE: We studied the secretion and action of glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) in young LBW men (n = 24) and matched normal birth weight controls (NBW) (n = 25). RESULTS: LBW subjects were 5 cm shorter but had a body mass index similar to NBW. LBW subjects had significantly elevated fasting and postprandial plasma glucose, as well as postprandial (standard meal test) plasma insulin and C-peptide concentrations, suggestive of insulin resistance. Insulin secretion in response to changes in glucose concentration ("beta-cell responsiveness") during the meal test was similar in LBW and NBW but inappropriate in LBW relative to insulin sensitivity. Fasting and postprandial plasma GLP-1 and GIP levels were similar in the groups. First- and second-phase insulin responses were similar in LBW and NBW during a hyperglycemic clamp (7 mm) with infusion of GLP-1 or GIP, respectively, demonstrating normal action of these hormones on insulin secretion. CONCLUSION: Reduced secretion or action of GLP-1 or GIP does not explain a relative reduced beta-cell responsiveness to glucose or the slightly elevated plasma glucose concentrations observed in young LBW men.     

Effects of gastric bypass surgery on glucose absorption and metabolism during a mixed meal in glucose-tolerant individuals

Aims/hypothesis

Roux-en-Y gastric bypass surgery (RYGB) improves glucose tolerance in patients with type 2 diabetes, but also changes the glucose profile in response to a meal in glucose-tolerant individuals. We hypothesised that the driving force for the changed postprandial glucose profiles after RYGB is rapid entry of glucose into the systemic circulation due to modified gastrointestinal anatomy, causing hypersecretion of insulin and other hormones influencing glucose disappearance and endogenous glucose production.

Methods

We determined glucose absorption and metabolism and the rate of lipolysis before and 3 months after RYGB in obese glucose-tolerant individuals using the double-tracer technique during a mixed meal.

Results

After RYGB, the postprandial plasma glucose profile changed, with a higher peak glucose concentration followed by a faster return to lower than basal levels. These changes were brought about by changes in glucose kinetics: (1) a more rapid appearance of ingested glucose in the systemic circulation, and a concomitant increase in insulin and glucagon-like peptide-1 secretion; (2) postprandial glucose disappearance was maintained at a high rate for a longer time after RYGB. Endogenous glucose production was similar before and after surgery. Postoperative glucagon secretion increased and showed a biphasic response after RYGB. Adipose tissue basal rate of lipolysis was higher after RYGB.

Conclusions/interpretation

A rapid rate of absorption of ingested glucose into the systemic circulation, followed by increased insulin secretion and glucose disappearance appears to drive the changes in the glucose profile observed after RYGB, while endogenous glucose production remains unchanged.

Trial registration

ClinicalTrials.gov NCT01559792.

Funding

The study was part of the UNIK program: Food, Fitness & Pharma for Health and Disease (see www.foodfitnesspharma.ku.dk). Funding was received from the Novo Nordisk foundation and the Strategic Research Counsel for the Capital Area and Danish Research Agency. The primary investigator received a PhD scholarship from the University of Copenhagen, which was one-third funded by Novo Nordisk.     

Four weeks of near-normalisation of blood glucose improves the insulin response to glucagon-like peptide-1 and glucose-dependent insulinotropic polypeptide in patients with type 2 diabetes

Objective  The incretin effect is attenuated in patients with type 2 diabetes mellitus, partly as a result of impaired beta cell responsiveness to glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1). The aim of the present study was to investigate whether 4 weeks of near-normalisation of the blood glucose level could improve insulin responses to GIP and GLP-1 in patients with type 2 diabetes. Methods  Eight obese patients with type 2 diabetes with poor glycaemic control (HbA_1c 8.6 ± 1.3%), were investigated before and after 4 weeks of near-normalisation of blood glucose (mean blood glucose 7.4 ± 1.2 mmol/l) using insulin treatment. Before and after insulin treatment the participants underwent three hyperglycaemic clamps (15 mmol/l) with infusion of GLP-1, GIP or saline. Insulin responses were evaluated as the incremental area under the plasma C-peptide curve. Results  Before and after near-normalisation of blood glucose, the C-peptide responses did not differ during the early phase of insulin secretion (0–10 min). The late phase C-peptide response (10–120 min) increased during GIP infusion from 33.0 ± 8.5 to 103.9 ± 24.2 (nmol/l) × (110 min)⁻¹ (p < 0.05) and during GLP-1 infusion from 48.7 ± 11.8 to 126.6 ± 32.5 (nmol/l) × (110 min)⁻¹ (p < 0.05), whereas during saline infusion the late-phase response did not differ before vs after near-normalisation of blood glucose (40.2 ± 11.2 vs 46.5 ± 12.7 [nmol/l] × [110 min]⁻¹). Conclusions  Near-normalisation of blood glucose for 4 weeks improves beta cell responsiveness to both GLP-1 and GIP by a factor of three to four. No effect was found on beta cell responsiveness to glucose alone. ClinicalTrials.gov ID no.: NCT 00612950 Funding: This study was supported by The Novo Nordisk Foundation, The Medical Science Research Foundation for Copenhagen.     

Suppression by exendin (9–39)amide of glucagon-like peptide-1 insulinotropic action in rats infused with dimethyl ester of succinic acid

Glucagon-like peptide-1 (GLP-1) acts as a nutrient-dependent insulin-releasing agent, and its insulinotropic action is enhanced by nutrient secretagogues, such as the dimethyl ester of succinic acid (SAD). In the present study, a primed constant infusion of SAD (0.5 μmol followed by 0.25 μmol/min both per g of body wt) was found to increase plasma insulin concentration in fed anesthetized rats, to potentiate the B-cell secretory response to GLP-1 (0.5 pmol/g of body wt), and to unmask the hypoglycemic potential of the gastrointestinal hormone. In the SAD-infused rats, the infusion of exendin(9–39)amide (5.0 pmol/min per g of body wt), 1 min before and 3 min after GLP-1 injection, decreased plasma insulin concentration before GLP-1 injection, suppressed the B-cell secretory response to GLP-1, and both delayed and minimized its hypoglycemic action. It is proposed, therefore, that exendin (9–39)amide could represent a tool in the treatment of alimentary or reactive hypoglycemia.     

Effect of glucagon-like peptide-1 on gastric somatostatin and gastrin secretion in the rat

The effect of glucagon-like peptide-1 (GLP-1) amide on gastric somatostatin and gastrin secretion was investigated in the isolated, vascularly perfused rat stomach preparation. GLP-1 (7-36) amide, 10(-12) to 10(-7)M, dose-dependently increased gastric somatostatin release, achieving maximal stimulation (314 +/- 15% above basal) at the highest dose. The somatostatin response to 10(-8)M GLP-1 (7-36) amide was not affected by concomitant perfusion with tetrodotoxin. GLP-1 (1-36) amide did not affect somatostatin release. Both basal and acetylcholine-stimulated gastrin were inhibited by GLP-1 (7-36) amide but were not influenced by GLP-1 (1-36) amide. In is concluded that GLP-1 (7-36) amide is the biologically effective peptide that stimulates gastric somatostatin and inhibits gastrin secretion, probably via non-neural pathways. GLP-1 (7-36) amide-induced inhibition of gastric acid secretion may, at least in part, be due to enhanced somatostatin and/or decreased gastrin release.     

Emptying of the gastric substitute,glucagon-like peptide-1 (GLP-1), and reactive hypoglycemia after total gastrectomy

Postprandial glucagon-like peptide-1 (GLP-1), pancreatic glucagon, and insulin were measured in 27 tumor-free patients 43 months (median) after total gastrectomy and in four controls using a⁹⁹technetium-labeled 100-g carbohydrate solid test meal. Emptying of the gastric substitute was measured by scintigraphy. Fourteen patients suffered from early dumping symptoms, and five of them also reported symptoms suggestive of reactive hypoglycemia (late dumping). The median emptying half-time (T1/2) of the gastric substitute was 480 sec. Sigstad's dumping score was 8.5±1.6 (mean±se) in patients with rapid emptying (T1/2<480 sec), and 3.0±1.5 in patients with slow emptying of the gastric substitute (P=0.02). The peak postprandial concentration of GLP-1 was 44±20 pmol/liter in controls, 172±50 in patients without reactive hypoglycemia, and 502±116 in patients whose glucose fell below 3.8 mmol/liter during the second postprandial hour. Plasma GLP-1 concentrations peaked at 15 min, and insulin concentrations at 30 min after the end of the meal. A close correlation between integrated GLP-1 responses and integrated insulin responses (r=0.68) was observed. Multiple regression revealed that three factors were significantly associated with the integrated glucose concentrations during the second hour (60–120 min): Early (first 30 min) integrated GLP-1 (inverse correlation;P=0.006), age (P=0.006), and early integrated pancreatic glucagon (P=0.005). There was a close (inverse) relationship ofT1/2 with early integrated GLP-1 and pancreatic glucagon, but not with insulin. Gel filtration of pooled postprandial plasma of gastrectomized individuals revealed that all glucagon-like immunoreactivity eluted atK _d 0.30 (K _d , coefficient of distribution), the elution position of glicentin. Almost all of the GLP-1 like immunoreactivity eluted atK _d 0.60, the elution position of gut GLP-1. The authors contend that GLP-1-induced insulin release and inhibition of pancreatic glucagon both contribute to the reactive hypoglycemia encountered in some patients following gastric surgery. Rapid emptying seems to be one causative factor for the exaggerated GLP-1 release in these subjects.     

Lack of effect of exendin-4 and glucagon-like peptide-1-(7,36)-amide on insulin action in non-diabetic humans

AIMS/HYPOTHESIS: The aim of this study was to determine whether rapid conversion to inactive and potentially antagonistic peptides could alter the response to GLP-1. METHODS: We evaluated the ability of exendin-4, a GLP-1 analogue resistant to degradation by dipeptidyl peptidase IV, to modulate insulin-induced stimulation of glucose uptake and suppression of glucose production in eight healthy subjects during infusion of GLP-1 (1.2 pmol.kg(-1).min(-1)), exendin-4 (0.12 pmol.kg(-1).min(-1)), or saline. Glucose was clamped at 5.3 mmol/l and insulin was infused to progressively increase insulin concentrations to about 65, 190 and 700 pmol/l, respectively. Endogenous insulin secretion was inhibited with somatostatin to ensure comparable portal insulin concentrations while glucagon and growth hormone were maintained at basal concentrations. RESULTS: Glucose, insulin, C-peptide, glucagon and growth hormone concentrations did not differ on the three occasions. In contrast, cortisol concentrations were greater during both exendin-4 (25.1+/-4.4 mmol/l per 7 h; p<0.01) and GLP-1, (17.0+/-2.0 mmol/l 7 h; p<0.05) than saline (13.5+/-1.5 mmol/l per 7 h). While insulin-induced stimulation of glucose disappearance at the highest insulin concentrations tended to be greater and insulin-induced suppression of glucose production lower in the presence of exendin-4 or GLP-1 than saline, the differences were not significant. CONCLUSION/INTERPRETATION: Exendin-4 and GLP-1 increase cortisol secretion in human subjects. However, neither alters insulin action in non-diabetic human subjects. These data also suggest that the lack of an effect of GLP-1 on insulin action is not likely to be explained by rapid degradation to inactive or antagonistic peptides.     

肠易激综合征模型大鼠血清胰高糖素样肽-1及结肠组织中其受体的变化

目的 观察肠易激综合征( IBS)不同亚型模型大鼠血清胰高糖素样肽(GLP)-1及结肠组织中GLP-1受体的变化,初步探讨GLP-1及其受体在IBS发病中的作用.方法 40只雄性SD大鼠均分为腹泻型IBS(D-IBS)模型组、灌肠对照组、便秘型IBS(C-IBS)模型组、灌胃对照组及空白对照组.乙酸加束缚应激法制备D-IBS模型,冰水灌胃法制备C-IBS模型.观察大鼠粪便变化,检测粪便重量、粪便含水量及大鼠小肠推进率,给予结直肠扩张(CRD)刺激,记录腹外斜肌放电活动(EMG),评价模型大鼠的内脏敏感性.酶联免疫法测定各组大鼠血清中活性GLP-1的含量.免疫组织化学法、实时定量PCR法及Western印迹法检测各组大鼠近端结肠及远端结肠组织中GLP-1 受体的分布和表达.结果 与各自的对照组及空白对照组相比,D-IBS模型组大鼠粪便湿重、粪便含水量及小肠推进率均上升(P＜0.05);C-IBS模型组粪便湿重、粪便含水量及小肠推进率均降低(P＜0.05).在压力为20、40及60 mm Hg(1 mm Hg=0.133 kPa)的结直肠扩张刺激下各模型组大鼠腹外斜肌放电幅值均较各对照组明显增加,且D-IBS模型组高于C-IBS模型组(P＜0.05).C-IBS模型组血清中活性GLP-1的水平高于D-IBS模型组(P＜0.05),IBS模型组和对照组之间差异无统计学意义.GLP-1受体主要分布在结肠黏膜组织、环肌层及肌间神经丛中.C-IBS模型组结肠组织中GLP-1受体mRNA及蛋白表达量显著高于灌胃对照组,D-IBS模型组结肠组织中表达量低于灌肠对照组(P＜0.05).结论 不同亚型IBS结肠组织中GLP-1受体的表达水平不同,血清GLP-1水平也不同,提示GLP-1及其受体的改变可能与IBS不同亚型的发生有关.     

胰高血糖素样肽-1对肥胖2型糖尿病大鼠胰岛素敏感性的改善作用

目的探讨胰高血糖素样肽(GLP)-1对肥胖2型糖尿病(T2DM)大鼠胰岛素敏感性的改善作用及机制。方法 12只6周龄雄性SD大鼠随机分为T2DM组、T2DM+GLP-1组及正常对照组(NC组)。T2DM组及T2DM+GLP-1组高脂喂养、NC组普食喂养4 w,给予T2DM组及T2DM+GLP-1组链脲佐菌素(STZ)30 mg/kg腹腔注射建立T2DM模型。受试大鼠进行高胰岛素-正葡萄糖钳夹实验。T2DM+GLP-1组大鼠在钳夹实验前30 min开始持续输注GLP-1,检测钳夹实验120 min葡萄糖输注率及0、30、60、90、120 min血清胰岛素浓度。Wester印迹法测定大鼠腓肠肌丝氨酸/苏氨酸激酶(Akt)磷酸化水平。结果与NC组比较,T2DM组钳夹实验120 min葡萄糖输注率降低(P0.05),骨骼肌Akt磷酸化水平下降;与T2DM组比较,T2DM+GLP-1组钳夹实验120 min葡萄糖输注率增加(P0.05),骨骼肌Akt磷酸化水平升高;各组间胰岛素浓度变化无差异(P0.05)。结论 GLP-1可以增加平静状态T2DM大鼠葡萄糖摄取,改善骨骼肌的胰岛素敏感性,这一改善作用不依赖于胰岛素浓度的增加。     

Effects of truncated glucagon-like peptide-1 on pancreatic hormone release in normal conscious dogs

The effects of truncated glucagon-like peptide-1 (GLP-1) on insulin and glucagon release were examined in unanesthetized normal dogs. A bolus injection of GLP-1(7-36)amide elicited a transient increase in the plasma insulin level, which brought about a decrease in the plasma glucose level. The degree of increase in plasma insulin levels with GLP-1(7-35)OH or GLP-1(7-37)OH was less than that induced by GLP-1(7-36)amide. The plasma glucagon level did not increase in spite of mild hypoglycemia. The infusion of graded doses of GLP-1(7-36)amide (6, 36, 120 ng.kg-1.min-1 every 30 min) did not change the plasma glucose, insulin or glucagon levels significantly. The degree of increase in the plasma glucose level induced by iv glucose infusion (12 mg.kg-1.min-1) was reduced by coinfusion of GLP-1(7-36)amide (6 ng.kg-1.min-1), although the degree of increase in the plasma insulin level was the same as that in a control experiment (coinfusion of the vehicle). Coinfusion of GLP-1(7-36)amide (60 ng.kg-1.min-1) caused an augmented increase in the plasma insulin level and a reduced increase in the plasma glucose level during iv glucose infusion (17 mg.kg-1.min-1) compared with the control experiment. The degree of decrease in the plasma glucagon level during iv glucose infusion was not affected by the coinfusion. The degree of increase in the plasma glucagon level induced by insulin hypoglycemia and the profile of the plasma glucose level at that time were not affected by the infusion of GLP-1(7-36)amide.(ABSTRACT TRUNCATED AT 250 WORDS)