Inositolphosphoglycans possibly mediate the effects of glucagon-like peptide-1(7-36)amide on rat liver and adipose tissue

Insulin-like effects of glucagon-like peptide-1(7-36)amide (GLP-1) in rat liver, skeletal muscle and fat, and also the presence of GLP-1 receptors in these extrapancreatic tissues, have been documented. In skeletal muscle and liver, the action of GLP-1 is not associated with an activation of adenylate cyclase, and in cultured murine myocytes and hepatoma cell lines, it was found that GLP-1 provokes the generation of inositolphosphoglycan molecules (IPGs), which are considered second messengers of insulin action. In the present work, we document in isolated normal rat adipocytes and hepatocytes that GLP-1 exerts a rapid decrease of the radiolabelled glycosylphosphatidylinositols (GPIs)—precursors of IPGs—in the same manner as insulin, indicating their hydrolysis and the immediate short-lived generation of IPGs. Thus, IPGs could be mediators in the GLP-1 actions in adipose tissue and liver, as well as in skeletal muscle, through GLP-1 receptors which are, at least functionally, different from that of the pancreatic B-cell. © 1998 John Wiley & Sons, Ltd.     

Degradation and glycemic effects of His(7)-glucitol glucagon-like peptide-1(7-36)amide in obese diabetic ob/ob mice

Glucagon-like peptide-1(7-36)amide (tGLP-1) has attracted considerable potential as a possible therapeutic agent for type 2 diabetes. However, tGLP-1 is rapidly inactivated in vivo by the exopeptidase dipeptidyl peptidase IV (DPP IV), thereby terminating its insulin releasing activity. The present study has examined the ability of a novel analogue, His(7)-glucitol tGLP-1 to resist plasma degradation and enhance the insulin-releasing and antihyperglycemic activity of the peptide in 20-25-week-old obese diabetic ob/ob mice. Degradation of native tGLP-1 by incubation at 37 degrees C with obese mouse plasma was clearly evident after 3 h (35% intact). After 6 h, more than 87% of tGLP-1 was converted to GLP-1(9-36)amide and two further N-terminal fragments, GLP-1(7-28) and GLP-1(9-28). In contrast, His(7)-glucitol tGLP-1 was completely resistant to N-terminal degradation. The formation of GLP-1(9-36)amide from native tGLP-1 was almost totally abolished by addition of diprotin A, a specific inhibitor of DPP IV. Effects of tGLP-1 and His(7)-glucitol tGLP-1 were examined in overnight fasted obese mice following i.p. injection of either peptide (30 nmol/kg) together with glucose (18 mmol/kg) or in association with feeding. Plasma glucose was significantly lower and insulin response greater following administration of His(7)-glucitol tGLP-1 as compared to glucose alone. Native tGLP-1 lacked antidiabetic effects under the conditions employed, and neither peptide influenced the glucose-lowering action of exogenous insulin (50 units/kg). Twice daily s.c. injection of ob/ob mice with His(7)-glucitol tGLP-1 (10 nmol/kg) for 7 days reduced fasting hyperglycemia and greatly augmented the plasma insulin response to the peptides given in association with feeding. These data demonstrate that His(7)-glucitol tGLP-1 displays resistance to plasma DPP IV degradation and exhibits antihyperglycemic activity and substantially enhanced insulin-releasing action in a commonly used animal model of type 2 diabetes.     

Microwave-assisted solid phase synthesis, PEGylation, and biological activity studies of glucagon-like peptide-1(7-36) amide

The insulinotropic hormone glucagon-like peptide-1 (GLP-1) is rapidly inactivated in the body. In order to improve its stability, we replaced the enzymatic hydrolyzation position Ala(8)with Gly and replaced Ala(30) with Cys firstly. Then the modified peptide was further PEGylated at thiol group of Cys(30). Biological activity studies showed that the resulting mPEG-MAL-Gly(8)-Cys(30)-GLP-1(7-36)-NH(2) exhibited long-lasting effect while maintaining moderate glucose-lowering activity.     

Vasorelaxant effect of glucagon-like peptide-(7-36)amide and amylin on the pulmonary circulation of the rat.

The gastrointestinal peptides glucagon-like peptide-1(7-36)amide (GLP-1) and amylin are currently being tested in clinical trials for the treatment of diabetes mellitus due to their effects in lowering blood glucose. Receptors for these polypeptides also exist in the lung and since polypeptides are known to modulate airway and pulmonary vascular tone, we investigated whether GLP-1 and amylin act similarly in the lung. We compared their effects with the well-known actions of calcitonin gene-related peptide (CGRP) and vasoactive intestinal peptide (VIP). Both GLP-1 and amylin induced a dose-dependent and time-reversible endothelial-dependent relaxation of preconstricted pulmonary artery rings. Amylin was approximately as strong as VIP and CGRP, GLP-1 however, was 2.3-fold less potent. GLP-1 as well as amylin also reduced the vascular tone in the isolated, perfused and ventilated rat lung. In contrast to their action on the pulmonary vasculature, neither GLP-1 nor amylin showed any effect on the tone of isolated preconstricted trachea rings. In conclusion, GLP-1 and amylin represent two additional peptides which may modulate pulmonary vascular tone.     

N-terminally modified glucagon-like peptide-1(7-36) amide exhibits resistance to enzymatic degradation while maintaining its antihyperglycaemic activity in vivo

Glucagon-like peptide-1(7-36)amide (tGLP-1) is inactivated by dipeptidyl peptidase (DPP) IV by removal of the NH(2)-terminal dipeptide His(7)-Ala(8). We examined the degradation of NH(2)-terminally modified His(7)99% of His(7)-glucitol tGLP-1 remained intact at 12 h. His(7)-glucitol tGLP-1 was similarly resistant to plasma degradation in vitro. His(7)-glucitol tGLP-1 showed greater resistance to degradation in vivo (92% intact) compared to tGLP-1 (27% intact) 10 min after i.p. administration to Wistar rats. Glucose homeostasis was examined following i.p. injection of both peptides (12 nmol/kg) together with glucose (18 mmol/kg). Plasma glucose concentrations were significantly reduced and insulin concentrations elevated following peptides administration compared with glucose alone. The area under the curve (AUC) for glucose for controls (AUC 691+/-35 mM/min) was significantly lower after administration of tGLP-1 and His(7)-glucitol tGLP-1 (36 and 49% less; AUC 440+/-40 and 353+/-31 mM/min, respectively; P<0.01). This was associated with a significantly higher AUC for insulin (98-99% greater; AUC 834+/-46 and 838+/-39 ng/ml/min, respectively; P<0.01) after tGLP-1 and His(7)-glucitol tGLP-1 administration compared to controls (421+/-30 ng/ml/min). In conclusion, His(7)-glucitol tGLP-1 resists plasma DPP IV degradation while retaining potent antihyperglycaemic and insulin-releasing activities in vivo.     

Effects of substitution of N-terminal amino acid of glucagon-like peptide-1 (7-36) amide on food intake of the neonatal chick

Glucagon-like peptide-1 (GLP-1), a member of glucagon superfamily, is synthesized from a large precursor, preproglucagon, and has been postulated to be a novel incretin. Recently, it was reported that central administration of GLP-1 (7-36) amide decreased food intake in rats and chickens. Generally, the amino acid sequences of the glucagon superfamily members except for gastric inhibitory peptide and growth hormone-releasing factor are identical at N-terminal histidine. It is well known that the GLP-1 receptor is highly specific for GLP-1 and does not bind other peptides of the glucagon superfamily. The aim of this study was to elucidate whether central injection of substituted GLP-1 in which N-terminal histidine of mammalian GLP-1 (7-36) amide was replaced with tyrosine, inhibits food intake in the chick. Intracerebroventricular administration of substituted GLP-1 inhibits food intake in the chick, although the effect of substituted GLP-1 was 11 to 13 fold less than that of mammalian GLP-1 (7-36) amide. These results indicate that N-terminal histidine of GLP-1 (7-36) amide is important for efficacy, but not essential for its bioactivity.     

Recombinant glucagon-like peptide-1 (7-36 amide) lowers fasting serum glucose in a broad spectrum of patients with type 2 diabetes.

AIMS: To evaluate the safety and efficacy of various doses of recombinant glucagon-like peptide-1 (7-36) amide (rGLP-1) administered subcutaneously (s. c.) via bolus injection or continuous infusion to lower fasting serum glucose (FSG) levels in subjects with type 2 diabetes treated by diet, hypoglycemic drugs, or insulin injection. METHODS: rGLP-1 was administered s. c. to 40 type 2 diabetics currently treated by diet, sulfonylurea (SU), metformin, or insulin in a double-blind, placebo-controlled, cross-over trial; preexisting treatments were continued during the study. In the bolus injection protocol, 32 subjects (8 from each of the 4 treatment groups) received 0.0, 0.5, 1.0, and 1.5 nmol rGLP-1/kg per injection (two injections, two hours apart, beginning one hour after the evening meal) in a randomized order on separate days. In the continuous s. c. infusion protocol, 40 subjects received rGLP-1 at 0.0, 1.5, 2.5, 3.5, and 4.5 pmol/kg/min for 10-12 hours overnight starting one hour after the evening meal. Fasting bloods were taken the morning after for glucose, insulin, and glucagon measurements. RESULTS: In the diet, SU, and metformin cohorts, bolus rGLP-1 injections produced modest reductions in mean FSG levels, averaging 17.4 mg/dl (7.3-27.5; 95 % CI) at the highest dose (p < 0.001 vs. placebo). Reductions in FSG levels were greater by continuous infusion at up to 30.3 mg/dl (18.8 - 41.8; 95 % CI; p < 0.001 vs. placebo). The greatest reduction in mean FSG occurred in the SU cohort (up to 43.9 mg/dl, 24.7 - 63.1; 95 % CI; p < 0.001). rGLP-1 infusions resulted in significant increases in fasting plasma insulin and decreases in fasting plasma glucagon levels. There were no serious adverse events; GI-related symptoms were dose-related and more commonly associated with injections. CONCLUSIONS: rGLP-1 (7-36) amide dose-dependently lowered FSG in a broad spectrum of type 2 diabetics when added to their existing treatment. Subcutaneous infusion was more effective than injection, and the combination with SU was more effective than with metformin.     

Priming effect of glucagon-like peptide-1 (7-36) amide, glucose-dependent insulinotropic polypeptide and cholecystokinin-8 at the isolated perfused rat pancreas.

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.     

The glucagon-like peptide-1 metabolite GLP-1-(9-36) amide reduces postprandial glycemia independently of gastric emptying and insulin secretion in humans

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.     

Expression of glucagon-like peptide-1 (GLP-1) receptor and the effect of GLP-1-(7-36) amide on insulin release by pancreatic islets during rat ontogenic development.

The expression of glucagon-like peptide-1 (GLP-1) receptor and the effects of GLP-1-(7-36) amide (t-GLP-1) on glucose metabolism and insulin release by pancreatic islets during rat development were studied. GLP-1 receptor mRNA was found in significant amounts in pancreatic islets from all age groups studied, GLP-1 receptor expression being maximal when pancreatic islets were incubated at physiological glucose concentration (5.5 mM), but decreasing significantly when incubated with either 1.67 or 16.7 mM glucose. Glucose utilization and oxidation by pancreatic islets from fetal and adult rats rose as a function of glucose concentration, always being higher in fetal than in adult islets. The addition of t-GLP-1 to the incubation medium did not modify glucose metabolism but gastric inhibitory polypeptide and glucagon significantly increased glucose utilization by fetal and adult pancreatic islets at 16.7 mM glucose. At this concentration, glucose produced a significant increase in insulin release by the pancreatic islets from 10-day-old and 20-day-old suckling rats and adult rats, whereas those from fetuses showed only a significant increase when glucose was raised from 1.67 to 5.5 mM. t-GLP-1 elicited an increase in insulin release by pancreatic islets from all the experimental groups when the higher glucose concentrations were used. Our findings indicate that GLP-1 receptors and the effect of t-GLP-1 on insulin release are already present in the fetus, and they therefore exclude the possibility that alterations in the action of t-GLP-1 are responsible for the unresponsiveness of pancreatic beta cells to glucose in the fetus, but stimulation of t-GLP-1 release by food ingestion in newborns may partially confer glucose competence on beta cells.     

New screening strategy and analysis for identification of allosteric modulators for glucagon-like peptide-1 receptor using GLP-1 (9-36) amide

The glucagon-like peptide-1 receptor (GLP-1R) is an important physiologic regulator of insulin secretion and a major therapeutic target for diabetes mellitus. GLP-1 (7-36) amide (active form of GLP-1) is truncated to GLP-1 (9-36) amide, which has been described as a weak agonist of GLP-1R and the major form of GLP-1 in the circulation. New classes of positive allosteric modulators (PAMs) for GLP-1R may offer improved therapeutic profiles. To identify these new classes, we developed novel and robust primary and secondary high-throughput screening (HTS) systems in which PAMs were identified to enhance the GLP-1R signaling induced by GLP-1 (9-36) amide. Screening enabled identification of two compounds, HIT-465 and HIT-736, which possessed new patterns of modulation of GLP-1R. We investigated the ability of these compounds to modify GLP-1R signaling enhanced GLP-1 (9-36) amide- and/or GLP-1 (7-36) amide-mediated cyclic adenosine monophosphate (cAMP) accumulation. These compounds also had unique profiles with regard to allosteric modulation of multiple downstream signaling (PathHunter β-arrestin signaling, PathHunter internalization signaling, microscopy-based internalization assay). We found allosteric modulation patterns to be obviously different among HIT-465, HIT-736, and Novo Nordisk compound 2. This work may enable the design of new classes of drug candidates by targeting modulation of GLP-1 (7-36) amide and GLP-1 (9-36) amide.     

Urinary excretion of glucagon-like peptide 1 (GLP-1) 7-36 amide in human type 2 (non-insulin-dependent) diabetes mellitus.

The urinary excretion of insulinotropic glucagon-like peptide 1 (GLP-1) was investigated as an indicator of renal tubular integrity in 10 healthy subjects and in 3 groups of type 2 diabetic patients with different degrees of urinary albumin excretion rate. No significant difference emerged between the groups with respect to age of the patients, known duration of diabetes, metabolic control, BMI, or residual beta-cell pancreatic function. Endogenous creatinine clearance was significantly reduced under conditions of overt diabetic nephropathy, compared with normo and microalbuminuric patients (p < 0.01). Urinary excretion of GLP-1 was significantly higher in normoalbuminuric patients compared to controls (490.4 +/- 211.5 vs. 275.5 +/- 132.1 pg/min; p < 0.05), with further increase under incipient diabetic nephropathy conditions (648.6 +/- 305 pg/min; p < 0.01). No significant difference resulted, in contrast, between macroproteinuric patients and non-diabetic subjects. Taking all patients examined into account, a significant positive relationship emerged between urinary GLP-1 and creatinine clearance (p = 0.004). In conclusion, an early tubular impairment in type 2 diabetes would occur before the onset of glomerular permeability alterations. The tubular dysfunction seems to evolve with the development of persistent microalbuminuria. Finally, the advanced tubular involvement, in terms of urinary GLP1 excretion, under overt diabetic nephropathy conditions would be masked by severe concomitant glomerular damage with the coexistence of both alterations resulting in a peptide excretion similar to control subjects.     

Identification and characterization of glucagon-like peptide-1 7-36 amide-binding sites in the rat brain and lung

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.     

Effects of glucagon-like peptide 1 (7-36) amide and glucagon on amylin release from perfused rat pancreas.

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.     

GLP-1 (9-36) amide, cleavage product of GLP-1 (7-36) amide, is a glucoregulatory peptide

Objective: Glucagon‐like peptide‐1 (GLP‐1) (7–36) amide is a glucoregulatory hormone with insulinotropic and insulinomimetic actions. We determined whether the insulinomimetic effects of GLP‐1 are mediated through its principal metabolite, GLP‐1 (9–36) amide (GLP‐1m). Methods and Procedures: Glucose turnover during two, 2‐h, euglycemic clamps was measured in 12 lean and 12 obese (BMI <25 or >30 kg/m²) male and female subject volunteers with normal oral glucose tolerance test. Saline or GLP‐1m were infused from 0 to 60 min in each study. Additionally, seven lean and six obese subjects underwent a third clamp in which the GLP‐1 receptor (GLP‐1R) antagonist, exendin (9–39) amide was infused from ?60 to 60 min with GLP‐1m from 0 to 60 min. Results: No glucose infusion was required in lean subjects to sustain euglycemia (glucose clamp) during saline or GLP‐1m infusions. However, in obese subjects glucose infusion was necessary during GLP‐1m infusion alone in order to compensate for a marked (>50%) inhibition of hepatic glucose production (HGP). Plasma insulin levels remained constant in lean subjects but rose significantly in obese subjects after termination of the peptide infusions. During GLP‐1R blockade, infusion of glucose was immediately required upon starting GLP‐1m infusions in all subjects due to a more dramatic reduction in HGP, as well as a delayed and modest insulinotropic response. Discussion: We conclude that GLP‐1m potently inhibits HGP and is a weak insulinotropic agent. These properties are particularly apparent and pronounced in obese but only become apparent in lean subjects during GLP‐1 (7–36) receptor blockade. These previously unrecognized antidiabetogenic actions of GLP‐1m may have therapeutic usefulness.     

Effect of nutrient ingestion on glucagon-like peptide 1 (7-36 amide) secretion in human type 1 and type 2 diabetes.

Exogenous glucagon-like peptide 1(GLP-1) bioactivity is preserved in type 2 diabetic patients, resulting the peptide administration in a near-normalization of plasma glucose mainly through its insulinotropic effect. GLP-1 also reduces meal-related insulin requirement in type 1 diabetic patients, suggesting an impairment of the entero-insular axis in both diabetic conditions. To investigate this metabolic dysfunction, we evaluated endogenous GLP-1 concentrations, both at fasting and in response to nutrient ingestion, in 16 type 1 diabetic patients (age = 40.5 +/- 14yr, HbA1C = 7.8 +/- 1.5%), 14 type 2 diabetics (age = 56.5 +/- 13yr, HbA1C = 8.1 +/- 1.8%), and 10 matched controls. In postabsorptive state, a mixed breakfast (230 KCal) was administered to all subjects and blood samples were collected for plasma glucose, insulin, C-peptide and GLP-1 determination during the following 3 hours. In normal subjects, the test meal induced a significant increase of GLP-1 (30', 60': p < 0.01), returning the peptide values towards basal concentrations. In type 2 diabetic patients, fasting plasma GLP-1 was similar to controls (102.1 +/- 1.9 vs. 97.3 +/- 4.01 pg/ml), but nutrient ingestion failed to increase plasma peptide levels, which even decreased during the test (p < 0.01). Similarly, no increase in postprandial GLP-1 occurred in type 1 diabetics, in spite of maintained basal peptide secretion (106.5 +/- 1.5 pg/ml). With respect to controls, the test meal induced in both diabetic groups a significant increase in plasma glucagon levels at 60' (p < 0.01). In conclusion, either in condition of insulin resistance or insulin deficiency chronic hyperglycemia, which is a common feature of both metabolic disorders, could induce a progressive desensitization of intestinal L-cells with consequent peptide failure response to specific stimulation.     

Glucagon-like peptide-1 (7-36) amide prevents the accumulation of pyruvate and lactate in the ischemic and non-ischemic porcine myocardium

Glucagon-like peptide-1 (7-36) amide (GLP-1) has been studied as a treatment option in diabetic patients. We investigated the effect of recombinant GLP-1 infusion on hemodynamic parameters, myocardial metabolism, and infarct size during normoxic conditions as well as during ischemia and reperfusion using an open-chest porcine heart model. In the presence of rGLP-1, interstitial levels of pyruvate and lactate decreased during ischemia and reperfusion both in ischemic and non-ischemic tissue. Moreover, rGLP-1 infusion resulted in increased plasma insulin levels and decreased blood glucose levels. Neither hemodynamic variables nor the consequent infarct size were influenced by rGLP-1 infusion. We conclude that rGLP-1 altered myocardial glucose utilization during ischemia and reperfusion. It did not exert any untoward hemodynamic effects.     

Glucagonlike peptide-1(7-36)amide suppresses glucagon secretion and decreases cyclic AMP concentration in cultured In-R1-G9 cells.

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.     

Immunoneutralization of endogenous glucagon-like peptide-2 reduces adaptive intestinal growth in diabetic rats

Supraphysiological doses of glucagon-like peptide-2 (GLP-2) have been shown to induce intestinal growth by increasing villus height and crypt depth and by decreasing apoptosis, but a physiological effect of GLP-2 has not yet been demonstrated. Earlier, we found elevated levels of endogenous GLP-2 in untreated streptozotocin diabetic rats associated with marked intestinal growth. In the present study, we investigated the role of endogenous GLP-2 for this adaptive response. We included four groups of six rats: (1) diabetic rats treated with saline, (2) diabetic rats treated with non-specific antibodies, (3) diabetic rats treated with polyclonal GLP-2 antibodies and (4) non-diabetic control rats treated with saline. All animals were treated with once daily intraperitoneal injections for 13 days and killed on day 14. Diabetic rats treated with saline or non-specific antibodies had a significantly (P<0.01) increased area of mucosa (13.00+/-0.64 and 13.37+/-0.60 mm(2), respectively) in the proximal part of the small intestine compared with non-diabetic controls (7.97+/-0.70 mm(2)). In contrast, diabetic rats treated with GLP-2 antibodies had a significantly (P<0.01) smaller increase in area of mucosa in the proximal part of the small intestine (10.84+/-0.44 mm(2)). Antibody treatment had no effect on body weight, blood glucose concentrations and food intake. Thus, blocking of endogenous GLP-2 in a model of adaptive intestinal growth reduces the growth response, providing strong evidence for a physiological growth factor function of GLP-2.