Chronic treatment with exendin(9–39)amide indicates a minor role for endogenous glucagon-like peptide-1 in metabolic abnormalities of obesity-related diabetes in ob/ob mice

in Journal of Endocrinology

Glucagon-like peptide-1 (GLP-1) is a potent insulinotropic hormone proposed to play a role in both the pathophysiology and treatment of type 2 diabetes. This study has employed the GLP-1 receptor antagonist, exendin-4(9–39)amide (Ex(9–39)) to evaluate the role of endogenous GLP-1 in genetic obesity-related diabetes and related metabolic abnormalities using ob/ob and normal mice. Acute in vivo antagonistic potency of Ex(9–39) was confirmed in ob/ob mice by blockade of the insulin-releasing and anti-hyperglycaemic actions of intraperitoneal GLP-1. In longer term studies, ob/ob mice were given once daily injections of Ex(9–39) or vehicle for 11 days. Feeding activity, body weight, and both basal and glucose-stimulated insulin secretion were not significantly affected by chronic Ex(9–39) treatment. However, significantly elevated basal glucose concentrations and impaired glucose tolerance were evident at 11 days. These disturbances in glucose homeostasis were independent of changes of insulin sensitivity and reversed by discontinuation of the Ex(9–39) for 9 days. Similar treatment of normal mice did not affect any of the parameters measured. These findings illustrate the physiological extrapancreatic glucose-lowering actions of GLP-1 in ob/ob mice and suggest that the endogenous hormone plays a minor role in the metabolic abnormalities associated with obesity-related diabetes.

Abstract

Glucagon-like peptide-1 (GLP-1) is a potent insulinotropic hormone proposed to play a role in both the pathophysiology and treatment of type 2 diabetes. This study has employed the GLP-1 receptor antagonist, exendin-4(9–39)amide (Ex(9–39)) to evaluate the role of endogenous GLP-1 in genetic obesity-related diabetes and related metabolic abnormalities using ob/ob and normal mice. Acute in vivo antagonistic potency of Ex(9–39) was confirmed in ob/ob mice by blockade of the insulin-releasing and anti-hyperglycaemic actions of intraperitoneal GLP-1. In longer term studies, ob/ob mice were given once daily injections of Ex(9–39) or vehicle for 11 days. Feeding activity, body weight, and both basal and glucose-stimulated insulin secretion were not significantly affected by chronic Ex(9–39) treatment. However, significantly elevated basal glucose concentrations and impaired glucose tolerance were evident at 11 days. These disturbances in glucose homeostasis were independent of changes of insulin sensitivity and reversed by discontinuation of the Ex(9–39) for 9 days. Similar treatment of normal mice did not affect any of the parameters measured. These findings illustrate the physiological extrapancreatic glucose-lowering actions of GLP-1 in ob/ob mice and suggest that the endogenous hormone plays a minor role in the metabolic abnormalities associated with obesity-related diabetes.

Keywords:

Introduction

The incretin hormone glucagon-like peptide-1 (GLP-1) has potent insulinotropic effects on pancreatic β-cells, and further promotes glucose lowering by enhancing glucose uptake and glyconeogenesis in peripheral tissues (Valverde et al. 1994, Villaneuva-Penacarillo et al. 1994, O’Harte et al. 1997). In addition, GLP-1 is reported to significantly reduce food consumption through a central effect and by inhibition of gastric emptying, which ultimately generates weight loss (Turton et al. 1996, Larsen et al. 2001). Consequently, GLP-1 has been put forward as a potential drug candidate for type 2 diabetes mellitus, and GLP-1 analogues are currently undergoing clinical trials (Holz & Chepurny 2003).

Speculation about GLP-1 has brought renewed interest in the related peptide, exendin-4(1–39)amide (Ex(1–39)) (Eng et al. 1992) which binds and activates the GLP-1 receptor (Göke et al. 1993, Thorens et al. 1993). Ex(1–39) is 39 amino acid peptide produced in the salivary glands of Heloderma suspectum (the Gila monster) and which shares similar insulinotropic and glucose-lowering actions with GLP-1 (Greig et al. 1999, Young et al. 1999). Unlike GLP-1, which is rapidly degraded, Ex(1–39) is resistant to the action of dipeptidyl peptidase IV (DPP IV) and consequently has a prolonged biological action (Elahi et al. 1999). Chronic administration of Ex(1–39) improves glucose control in diabetic db/db mice (Greig et al. 1999), and reduces food intake and weight gain in Zucker fatty rats (Szayna et al. 2000). An analogue of Ex(1–39), AC2933, is currently being tested as an anti-diabetic drug (Holz & Chepurny 2003). However, the fact that Ex(1–39) is not a human physiological hormone and may trigger the immune system is something which should not be overlooked.

Interestingly, a truncated form of Ex(1–39), exendin(9–39)amide (Ex(9–39)), serves as a strong antagonist of the GLP-1 receptor, blocking the cellular and metabolic effects of GLP-1 (Göke et al. 1993, Thorens et al. 1993, Kolligs et al. 1995, Green et al. 2004). Acute studies have used Ex(9–39) to determine the contribution of GLP-1 to the incretin effect in normal animals (Kolligs et al. 1995, Tseng et al. 1999). These studies have revealed that GLP-1 is an important physiological insulin-releasing hormone, contributing 32–60% to the overall incretin effect.

The risk of developing type 2 diabetes, a disease clinically characterised by elevated blood glucose, impaired glucose tolerance, hyperglycaemia and insulin resistance, is greatly increased in obese individuals (Kolterman et al. 1981, Bogardus et al. 1985, Golay & Felber 1994). The role of the enteroinsular axis and GLP-1 in obesity-related diabetes remains uncertain (Ranganath et al. 1996, Flint et al. 2001, Vilsboll et al. 2003). However, recent opinion is that GLP-1 secretion may be disturbed, whereas action on pancreatic β-cells is normal (Mannucci et al. 2000, Vilsboll et al. 2001).

In this investigation Ex(9–39) was employed to molecularly disrupt the action of GLP-1 in adult obese diabetic (ob/ob) mice to assess the involvement of endogenous GLP-1 in the established hyperphagia, hyperinsulinaemia, glucose intolerance and related metabolic abnormalities of this commonly employed model of type 2 diabetes (Bailey & Flatt 2003). Ex(9–39) was administered once daily for 11 days and the effects on feeding activity, body weight, glucose tolerance, pancreatic β-cell function and insulin sensitivity were recorded. These measurements were repeated after a 9-day recovery period to evaluate the effects of alleviation of GLP-1 receptor antagonism. Comparative studies were conducted in normal mice.

Materials and Methods

Reagents

Ex(9–39) was a gift from Dr Andrew Young (Amylin Corporation, San Diego, CA, USA). Na125I for iodination of insulin was obtained from Amersham International plc (Amersham, Bucks, UK). Bovine insulin, dextran-T70 and activated charcoal were obtained from Sigma (Poole, Dorset, UK). All other chemicals used were of the utmost purity available.

Animals

The genetic background and characteristics of the ob/ob (Lepob/Lepob) mouse colony and normal control homozygous (+/+) mice have been outlined elsewhere (Bailey et al. 1982). Briefly, heterozygous C57BL/6J ob/+ breeding pairs from the Jackson Laboratory, Bar Harbor, Maine, USA were obtained by the Institute of Animal Genetics, University of Edinburgh in 1957 and out-crossed to non-inbred local strains: JH for higher litter size and CRL for higher growth rate. Heterozygous breeding pairs from this stock were obtained by Aston University in 1966 where they have been maintained in a closed non-inbred colony. The Aston colony of (ob/ob) mice display hyperphagia, marked hyperinsulinaemia, islet hypertrophy and moderate hyperglycaemia (Bailey & Flatt 1995).

Animals, aged 15–19 weeks, were housed individually in an air-conditioned room at 22 ± 2 °C with a 12 h light:12 h darkness cycle. Drinking water and a standard rodent maintenance diet (Trouw Nutrition Ltd, Cheshire, UK) were freely available. All animal experiments were carried out in accordance with the UK Animals (Scientific Procedures) Act 1986. No adverse effects were observed following administration of saline or Ex(9–39).

Acute effects of Ex(9–39) on GLP-1-mediated glucose lowering and insulin release

To confirm that Ex(9–39) acted as a functional GLP-1 receptor antagonist in this group of ob/ob mice, acute experiments were performed. Fasted (18 h) ob/ob mice were administered intraperitoneally with glucose alone (18 mmol/kg body weight) or in combination with 25 nmol/kg GLP-1 or 25 nmol/kg GLP-1 plus an equivalent dose of either GLP-1 or Ex(9–39). Plasma glucose and insulin levels were measured in blood samples taken prior to and at 15, 30 and 60 min after injection.

Long-term effects of Ex(9–39) on metabolism

Groups of ob/ob mice and normal control mice received once daily subcutaneous injections (1700 h) of either saline (0.9% (w/v) NaCl) or Ex(9–39) (25 nmol/kg in saline) over an 11-day period. The animals were also monitored for 9 days after the cessation of treatment. Food intake and body weight were recorded daily. Blood samples were collected on days 0, 1, 3, 7, 11, 14 and 20 (0900 h) from the cut tail tips of conscious mice. Glucose tolerance (18 mmol/kg, intraperitoneally), meal tolerance (15-min refeeding after an 18-h fast) and insulin sensitivity (50 U/kg, intraperitoneally) tests were conducted on day 11 and day 20. Blood samples were collected at the times indicated in the figures into chilled fluoride/heparin-coated microcentrifuge tubes (Sarstedt, Nümbrecht, Germany) and centrifuged (30s at 13 000g) using a Beckman microcentrifuge (Beckman Instruments, Palo Alto, CA, USA). The resulting plasma was then aliquoted into fresh Eppendorf tubes and stored at − 20 °C prior to analysis.

Analyses

Plasma glucose was assayed by an automated glucose oxidase procedure using a Beckman glucose analyser II (Stevens 1971). Plasma insulin was assayed by a modified dextran–charcoal radioimmunoassay (Flatt & Bailey 1981). In vivo data were compared using ANOVA, followed by the Student–Newman–Keuls post hoc test. Area under the curve (AUC) analysis employed the trapezoidal rule (Burington 1973). Groups of data from both were considered to be significantly different if P<0.05.

Results

Acute Ex(9–39) antagonism of GLP-1 action

Figure 1 shows the plasma glucose and insulin responses of ob/ob mice to glucose alone or in combination with either GLP-1 plus equipotent GLP-1 or Ex(9–39). As expected, administration of GLP-1 markedly decreased the glycaemic excursion (Fig. 1A) and enhanced insulin concentrations (Fig. 1B) compared with glucose alone. These actions of GLP-1 were substantially blocked by the established GLP-1-receptor antagonist, Ex(9–39) (Fig. 1A and B).

Long-term effects of Ex(9–39)

Figure 2 shows the effects of long-term Ex(9–39) treatment on body weight, food intake and plasma concentrations of glucose and insulin in ob/ob mice. Ex(9–39) had no significant effect on either body weight or food intake (Fig. 2A and B). However, on day 11 of treatment basal plasma glucose levels were significantly raised in mice treated with Ex(9–39), compared with those treated with saline (P<0.05; Fig. 2C). Cessation of treatment returned glucose to pretreatment levels. No significant changes in plasma insulin levels were noted during or after the treatment period, although there appeared to be a trend towards decreased concentrations with Ex(9–39) (Fig. 2D). Treatment of normal mice with Ex(9–39) did not affect any of the parameters measured (Fig. 3).

Long-term effects of Ex(9–39) treatment on glucose tolerance

Figure 4 shows the effects of intraperitoneal glucose administration (18 mmol/kg) on glucose and insulin levels in ob/ob mice treated for 11 days with either saline or Ex(9–39). Glucose levels in Ex(9–39)-treated mice were significantly elevated 0, 15, 30 and 60 min after injection compared with mice treated with saline alone (Fig. 4A). This was confirmed by a significantly increased AUC value (P<0.05; Fig. 4A). No significant changes in glucose-mediated insulin release were noted in mice treated with Ex(9–39) compared with those treated with saline (Fig. 4B). As shown in Fig. 5, no significant changes in plasma glucose or insulin levels were evident in ob/ob mice 9 days after cessation of Ex(9–39)-treatment. Treatment of normal mice with Ex(9–39) for 11 days did not significantly affect glycaemic or insulin responses to intraperitoneal glucose (Fig. 6). Responses of normal mice were identical 9 days following cessation of treatment (data not shown).

Long-term effects of Ex(9–39) treatment on metabolic response to feeding

Figure 7 shows the glucose and insulin responses of fasted (ob/ob) mice to feeding after 11 days of treatment with Ex(9–39). An allowed period of 15 min of feeding caused significant rises in both plasma glucose (Fig. 7A) and insulin (Fig. 7B). However, responses in saline-treated mice and Ex(9–39)-treated mice were not significantly different. Food intake during the 15-min period was consistent with these data, showing no significant difference in saline-treated (0.5 ± 0.1 g/mouse per 15 min) and Ex(9–39)-treated (0.6 ± 0.1 g/mouse per 15 min) mice. Similarly 11 days of treatment with Ex(9–39) did not affect glucose or insulin responses to feeding in normal mice (Fig. 8). Food intake was 0.5 ± 0.1 g/mouse per 15 min and 0.5 ± 0.1 g/mouse per 15 min for control and Ex(9–39) respectively.

Long-term effects of Ex(9–39) treatment on insulin sensitivity

Figure 9 shows the effect of intraperitoneal administration of insulin on glucose levels in ob/ob mice (Fig. 9A) and normal mice (Fig. 9B) following 11 days of treatment with Ex(9–39). No significant changes in insulin-induced glucose lowering were observed in animals receiving treatment or 9 days following the cessation of treatment (data not shown).

Discussion

Ex(1–39) is a 39 amino acid peptide isolated from Heloderma suspectum (Gila monster) venom (Eng et al. 1992). It later transpired that Ex(1–39) was a highly potent agonist of the GLP-1 receptor (Thorens et al. 1993). Furthermore, a shortened form of this peptide, Ex(9–39), possessed significant antagonistic activity for this receptor (Göke et al. 1993, Thorens et al. 1993). These findings have been confirmed many times in acute tests involving rat GLP-1 receptors, humans (Schirra et al. 1998, Edwards et al. 1999) and various non-diabetic and diabetic animal models (Kolligs et al. 1995, Wang et al. 1995, Gault et al. 2003, Green et al. 2004).

Although many studies have demonstrated acute antagonistic actions of Ex(9–39), the chronic effects of Ex(9–39) administration on insulin secretion and glucose homeostasis in animal models with established obesity-related diabetes such as ob/ob mice have not been evaluated. Given the beneficial effects of chronic administration of the GLP-1 receptor agonist, Ex(1–39), in db/db mice (Greig et al. 1999, Szayna et al. 2000), plus the role of GLP-1 in the enteroinsular axis, we anticipated that chronic administration of Ex(9–39) would have quite profound effects in ob/ob mice. This animal model is characterised by a less severe form of diabetes than db/db mice due to metabolic compensation through islet hypertrophy and marked hyperinsulinaemia (Bailey & Flatt 2003). In initial studies, we confirmed that this mutant displayed prominent insulin secretory and anti-hyperglycaemic responses to GLP-1 as described elsewhere (Green et al. 2004). Furthermore, administration of Ex(9–39) reduced the acute glucose-lowering action of GLP-1 by 70%, while the insulin-releasing action of GLP-1 was almost completely abolished (reduced by 95%). These results corroborated the findings of earlier investigations (Kolligs et al. 1995, Schirra et al. 1998, Edwards et al. 1999, Tseng et al. 1999, Green et al. 2004).

Administration of Ex(9–39) once daily for 11 days to ob/ob mice had no effect on feeding activity or body weight. Since GLP-1 is believed to exert satiety effects which can be reversed by Ex(9–39) in other species (Schick et al. 2003), this suggests that endogenous circulating GLP-1 has no such role in ob/ob mice. However, the present study did not note an inhibitory effect of Ex(9–39) on feeding in normal mice. Consistent with a limited physiological role for circulating GLP-1 in ob/ob mice, basal and glucose-stimulated insulin secretion were not significantly changed by chronic Ex(9–39) treatment. However, small impairments in glucose homeostasis were noted, namely elevated basal glucose and impaired glucose tolerance after 11 days. These effects were independent of changes in insulin sensitivity and reversed by discontinuation of Ex(9–39) for 9 days.

In contrast to ob/ob mice, administration of Ex(9–39) to normal mice for 11 days was without affect on glucose homeostasis or any of the other parameters measured. This showed that the modest effects in ob/ob mice cannot be directly attributed to leptin deficiency. These general observations have parallels with GLP-1 receptor knockout (GLP-1R−/−) mice which exhibit only a modest intolerance to glucose (Scrocchi et al. 1996, Flamez et al. 1998, Scrocchi & Drucker 1998). In these transgenic animals it appears likely that there was a compensatory increase in the glucose-dependent insulinotropic polypeptide (GIP) arm of the enteroinsular axis from early life (Pederson et al. 1998). Although a similar adaptive response might have been induced very rapidly by the present 11-day administration of Ex(9–39), there is presently no commercial assay to specifically measure active GIP(1–42) in small plasma volumes for mice. However, it is notable that the adverse effects on glucose homeostasis in ob/ob mice were not matched by any significant changes in insulin secretion. This supports the view that GLP-1 not only facilitates glucose lowering though glucose-dependent insulin release but also by a range of additional extrapancreatic effects (Valverde et al. 1994, Villanueva-Penacarillo et al. 1994, O’Harte et al. 1997).

Although rather little is known about concentrations of ‘active’ GLP-1 in the circulation and intestines of ob/ob mice, there are no appreciable differences compared with normal mice (Mooney et al. 2002, Anini & Brubaker 2003). Indeed, plasma concentrations of GLP-1 appear to be decreased generally in obesity due to insensitivity to the normal stimulatory effects of leptin (Ranganath et al. 1996, Anini & Brubaker 2003). Interestingly, higher levels of DPP IV activity have been reported in ob/ob mice compared with lean controls (Ruter et al. 2004), but the significance of this observation needs clarification. In sharp contrast, early studies indicate that the sister incretin hormone, GIP, is present in both the plasma and intestines of ob/ob mice at remarkably raised concentrations (Flatt et al. 1983, 1984). Taken together, these observations suggest a relatively minor role for circulating GLP-1 in the metabolic abnormalities of ob/ob mice. In contrast, GIP appears to be the major physiological component of the enteroinsular axis in these animals, as evidenced by acute blockade of GIP action with the receptor antagonist (Pro3)GIP (Gault et al. 2003). The established effects of GIP on insulin secretion and adipose tissue metabolism (Yip & Wolfe 2000) also indicate that markedly elevated GIP levels in this mutant contribute substantially to the characteristic hyperinsuliaemia, fat disposition and insulin resistance (Bailey & Flatt 2003).

In conclusion, this study has shown that prolonged antagonism of circulating GLP-1 in obese diabetic (ob/ob) mice with Ex(9–39) caused a slight impairment of glucose homeostasis without appreciable effects on food intake, pancreatic β-cell function or insulin sensitivity. No significant effects were observed in normal mice. These observations indicate a minor role for endogenous GLP-1 in the metabolic abnormalities of ob/ob mice and suggest that elevated concentrations of GIP make a major contribution to the obesity-related diabetes syndrome.

Figure 1
Figure 1

Acute effects of Ex(9–39) on GLP-1-induced glucose lowering and insulin release in ob/ob mice. Concentrations of (A) plasma glucose and (B) insulin prior to, and 15, 30 and 60 min after intraperitoneal administration of glucose alone (18 mmol/l per kg) or in combination with 25 nmol/kg GLP-1, 25 nmol/kg GLP-1 plus equimolar GLP-1 or 25 nmol/kg GLP-1 plus equimolar Ex(9–39). The time of injection is indicated by the arrows. Plasma glucose and plasma insulin AUC values for 0–60 min after injection are shown. Values are means ± s.e.m. for eight mice. *P<0.05, **P<0.01 and ***P<0.001 compared with glucose alone. ΔP<0.05, ΔΔP<0.01 and ΔΔΔP<0.001 compared with GLP-1 plus GLP-1.

Citation: Journal of Endocrinology 185, 2; 10.1677/joe.1.05876

Figure 2
Figure 2

Food intake, body weight and plasma glucose and insulin concentrations of ob/ob mice receiving 11 daily injections of either saline or Ex(9–39). (A) Body weight, (B) food intake, (C) plasma glucose and (D) plasma insulin concentrations were measured for 5 days prior to, for 11 days during (indicated by solid bars) and for 9 days after treatment with saline or Ex(9–39) (25 nmol/kg body weight). Values are means ± s.e.m. for eight mice. *P<0.05 compared with saline group.

Citation: Journal of Endocrinology 185, 2; 10.1677/joe.1.05876

Figure 3
Figure 3

Food intake, body weight and plasma glucose and insulin concentrations of normal mice receiving 11 daily injections of either saline or Ex(9–39). (A) Body weight, (B) food intake, (C) plasma glucose and (D) plasma insulin concentrations were measured for 5 days prior to, for 11 days during (indicated by solid bars) and for 9 days after treatment with saline or Ex(9–39) (25 nmol/kg body weight). Values are means ± s.e.m. for eight mice.

Citation: Journal of Endocrinology 185, 2; 10.1677/joe.1.05876

Figure 4
Figure 4

Long-term effects of Ex(9–39) treatment on glucose and insulin responses to intraperitoneal glucose administration in ob/ob mice. (A) Plasma glucose and (B) plasma insulin concentrations were measured prior to and at intervals after intraperitoneal administration of glucose (18 mmol/kg body weight) after 11 days of treatment with Ex(9–39). The time of injection is indicated by the arrows. Plasma glucose and plasma insulin AUC values for 0–60 min after injection are shown. Values are means ± s.e.m. for eight mice. *P<0.05 compared with saline.

Citation: Journal of Endocrinology 185, 2; 10.1677/joe.1.05876

Figure 5
Figure 5

Reversal of long-term effects of Ex(9–39) treatment on glucose and insulin responses to intraperitoneal glucose in ob/ob mice. (A) Plasma glucose and (B) plasma insulin concentrations were measured prior to and at intervals after intraperitoneal administration of glucose (18 mmol/kg body weight) 9 days after cessation of Ex(9–39) treatment. The time of injection is indicated by the arrows. Plasma glucose and plasma insulin AUC values for 0–60 min after injection are shown. Values are means ± s.e.m. for eight mice.

Citation: Journal of Endocrinology 185, 2; 10.1677/joe.1.05876

Figure 6
Figure 6

Long-term effects of Ex(9–39) treatment on glucose and insulin responses to intraperitoneal glucose administration in normal mice. (A) Plasma glucose and (B) plasma insulin concentrations were measured prior to and at intervals after intraperitoneal administration of glucose (18 mmol/kg body weight) after 11 days treatment with Ex(9–39). The time of injection is indicated by the arrows. Plasma glucose and plasma insulin AUC values for 0–60 min after injection are shown. Values are means ± s.e.m. for eight mice.

Citation: Journal of Endocrinology 185, 2; 10.1677/joe.1.05876

Figure 7
Figure 7

Long-term effects of Ex(9–39) treatment on glucose and insulin responses to feeding in ob/ob mice. Following the 11-day treatment period mice were fasted (18 h) overnight. At 0900 h, free access to food was allowed for 15 min (indicated by the solid bars) and (A) plasma glucose and (B) plasma insulin concentrations were measured. Plasma glucose and plasma insulin AUC values for 0–105 min after feeding are shown. Values are means ± s.e.m. for eight mice.

Citation: Journal of Endocrinology 185, 2; 10.1677/joe.1.05876

Figure 8
Figure 8

Long-term effects of Ex(9–39) treatment on glucose and insulin responses to feeding in normal mice. Following the 11-day treatment period mice were fasted (18 h) overnight. At 0900 h, free access to food was allowed for 15 min (indicated by the solid bars) and (A) plasma glucose and (B) plasma insulin concentrations were measured. Plasma glucose and plasma insulin AUC values for 0–105 min after feeding are shown. Values are means ± s.e.m. for eight mice.

Citation: Journal of Endocrinology 185, 2; 10.1677/joe.1.05876

Figure 9
Figure 9

Insulin sensitivity of (A) ob/ob mice and (B) normal mice chronically treated for 11 days with Ex(9–39). The time of injection is indicated by the arrows. Plasma glucose concentrations were measured prior to and at intervals after intraperitoneal administration of insulin (50U/kg body weight). Corresponding AUC values (0–60 min) for plasma glucose show overall effects to exogenous insulin administration.

Citation: Journal of Endocrinology 185, 2; 10.1677/joe.1.05876

These studies were supported by the Department of Health and Personal Social Services for Northern Ireland and the University of Ulster Strategy Research Funding. The authors declare that there is no conflict of interest that would prejudice the impartiality of this scientific work.

References

  • AniniY & Brubaker PL 2003 Role of leptin in the regulation of glucagon-like peptide-1 secretion. Diabetes52252–259.

  • BaileyCJ & Flatt PR 1995 Develepment of antidiabetic drugs. In Drugs Diet and Disease: Mechanistic Approaches to Diabetes pp 279–326. Eds C Ioanides & PR Flatt. London: Ellis Horwood.

  • BaileyCJ & Flatt PR 2003 Animal syndromes resembling type 2 diabetes. In Textbook of Diabetes edn 3 pp 25.1–25.30. Eds JC Pickup & G Williams. Oxford: Blackwell Scientific Publications.

  • BaileyCJ Flatt PR & Atkins TW 1982 Influence of genetic background and age on the expression of the obese hyperglycaemic syndrome in Aston ob/ob mice. International Journal of Obesity611–21.

    • Search Google Scholar
    • Export Citation
  • BogardusC Lillioja S Mott DM Hollenbeck C & Reaven G 1985 Relationship between degree of obesity and in vivo insulin action in man. American Journal of Physiology – Endocrinology and Metabolism248E286–E291.

    • Search Google Scholar
    • Export Citation
  • BuringtonRS1973Handbook of Mathematical Tables and Formulas. New York: McGraw-Hill.

  • EdwardsCM Todd JF Mahmoudi M Wang Z Wang RM Ghatei MA & Bloom SR 1999 Glucagon-like peptide 1 has a physiological role in the control of postprandial glucose in humans: studies with the antagonist exendin 9–39. Diabetes4886–93.

    • Search Google Scholar
    • Export Citation
  • ElahiD Clocquet A & Egan JM 1999 Exendin-4 is insulinotropic in non-diabetic and diabetic subjects. Diabetologia42148A.

  • EngJ Kleinman WA Singh L Singh G & Raufman JP 1992 Isolation and characterization of exendin-4 an exendin-3 analogue from Heloderma suspectum venom. Further evidence for an exendin receptor on dispersed acini from guinea pig pancreas. Journal of Biological Chemistry2677402–7405.

    • Search Google Scholar
    • Export Citation
  • FlamezD Van Breusegem A Scrocchi LA Quartier E Pipeleers D Drucker DJ & Schuit F 1998 Mouse pancreatic beta-cells exhibit preserved glucose competence after disruption of the glucagon-like peptide-1 receptor gene. Diabetes47646–652.

    • Search Google Scholar
    • Export Citation
  • FlattPR & Bailey CJ 1981 Abnormal plasma glucose and insulin responses in heterozygous lean (ob/+) mice. Diabetologia20573–577.

  • FlattPR Bailey CJ Kwasowski P Swanston-Flatt SK & Marks V 1983 Abnormalities of GIP in spontaneous syndromes of obesity and diabetes in mice. Diabetes32433–435.

    • Search Google Scholar
    • Export Citation
  • FlattPR Bailey CJ Kwasowski P Page P & Marks V 1984 Plasma immunoreactive gastric inhibitory polypeptide in obese hyperglycaemic (ob/ob) mice. Journal of Endocrinology101249–256.

    • Search Google Scholar
    • Export Citation
  • FlintA Raben A Ersboll AK Holst JJ & Astrup A 2001 The effect of physiological levels of glucagon-like peptide-1 on appetite gastric emptying energy and substrate metabolism in obesity. International Journal of Obesity and Related Metabolic Disorders25781–792.

    • Search Google Scholar
    • Export Citation
  • GaultVA Flatt CJ Harriott P Green BD & O’Harte FPM 2003 Effects of the novel (Pro3)GIP antagonist and exendin (9–39) amide GIP and GLP-1 induced cyclic AMP generation insulin secretion and postprandial insulin release in obese diabetic (ob/ob) mice: evidence that GIP is the major physiological incretin. Diabetologia46222–230.

    • Search Google Scholar
    • Export Citation
  • GökeR Fehmann HC Linn T Schmidt H Krause M Eng J & Göke B 1993 Exendin-4 is a high potency agonist and truncated exendin-(9–39)-amide an antagonist at the glucagon-like peptide 1-(7–36)-amide receptor of insulin-secreting beta-cells. Journal of Biological Chemistry26819650–19655.

    • Search Google Scholar
    • Export Citation
  • GolayA & Felber JP 1994 Evolution from obesity to diabetes. Diabetes Metabolism203–14.

  • GreenBD Mooney MH Gault VA Irwin N Bailey CJ Harriott P Greer B Flatt PR & O’Harte FPM 2004 Lys9 for Glu9 substitution in glucagon-like peptide-1(7–36)amide (GLP-1) confers DPP IV resistance with cellular and metabolic actions similar to those of established antagonists GLP-1(9–36)amide and exendin (9–39). Metabolism53252–259.

    • Search Google Scholar
    • Export Citation
  • GreigNH Holloway HW De Ore KA Jani D Wang Y Zhou J Garant MJ & Egan JM 1999 Once daily injection of exendin-4 to diabetic mice achieves long-term beneficial effects on blood glucose concentrations. Diabetologia4245–50.

    • Search Google Scholar
    • Export Citation
  • HolzGG & Chepurny OG 2003 Glucagon-like peptide-1 synthetic analogs: new therapeutic agents for use in the treatment of diabetes mellitus. Current Medicinal Chemistry102471–2483.

    • Search Google Scholar
    • Export Citation
  • KolligsF Fehmann HC Göke R & Göke B 1995 Reduction of the incretin effect in rats by the glucagon-like peptide 1 receptor antagonist exendin (9–39) amide. Diabetes4416–19.

    • Search Google Scholar
    • Export Citation
  • KoltermanOG Gray RS Griffin J Burstein P Insel J Scarlett JA & Olefsky JM 1981 Receptor and postreceptor defects contribute to the insulin resistance in non-insulin-dependent diabetes mellitus. Journal of Clinical Investigation68957–969.

    • Search Google Scholar
    • Export Citation
  • LarsenPJ Fledelius C Knudsen LB & Tang-Christensen M 2001 Systemic administration of the long-acting GLP-1 derivative NN2211 induces lasting and reversible weight loss in both normal and obese rats. Diabetes502530–2539.

    • Search Google Scholar
    • Export Citation
  • MannucciE Ognibene A Cremasco F Bardini G Mencucci A Pierazzuoli E Ciani S Fanelli A Messeri G & Rotella CM 2000 Glucagon-like peptide (GLP)-1 and leptin concentrations in obese patients with Type 2 diabetes mellitus. Diabetic Medicine10713–719.

    • Search Google Scholar
    • Export Citation
  • MooneyMH Abdel-Wahab YHA McKillop AM O’Harte FPM & Flatt PR 2002 Evaluation of glycated glucagon-like peptide-1(7–36)amide in intestinal tissues of normal and diabetic animal models. Biochimica et Biophysica Acta156975–80.

    • Search Google Scholar
    • Export Citation
  • O’HarteFPM Gray AM Abdel-Wahab YHA & Flatt PR 1997 Effects of non-glycated and glycated glucagon-like peptide-1(7–36) amide on glucose metabolism in isolated mouse abdominal muscle. Peptides181327–1333.

    • Search Google Scholar
    • Export Citation
  • PedersonRA Satkunarajah M McIntosh CH Scrocchi LA Flamez D Schuit F Drucker DJ & Wheeler MB 1998 Enhanced glucose-dependent insulinotropic polypeptide secretion and insulinotropic action in glucagon-like peptide 1 receptor −/− mice. Diabetes471046–1052.

    • Search Google Scholar
    • Export Citation
  • RanganathLR Beety JM Morgan LM Wright JW Howland R & Marks V 1996 Attenuated GLP-1 secretion in obesity: cause or consequence? Gut38916–919.

    • Search Google Scholar
    • Export Citation
  • RuterJ Hoffmann T Demuth HU Moschansky P Klapp BF & Hildebrandt M 2004 Evidence for an interaction between leptin T cell costimulatory antigens CD28 CTLA-4 and CD26 (dipeptidyl peptidase IV) in BCG-induced immune responses of leptin- and leptin receptor-deficient mice. Biological Chemistry385537–541.

    • Search Google Scholar
    • Export Citation
  • SchickRR Zimmermann JP vorm Walde T & Schusdziarra V 2003 Peptides that regulate food intake: glucagon-like peptide 1-(7–36) amide acts at lateral and medial hypothalamic sites to suppress feeding in rats. American Journal of Physiology – Regulatory Integrative and Comparative Physiology284R1427–R1435.

    • Search Google Scholar
    • Export Citation
  • SchirraJ Sturm K Leicht P Arnold R Göke B & Katschinski M 1998 Exendin(9–39)amide is an antagonist of glucagon-like peptide-1(7–36)amide in humans. Journal of Clinical Investigation1011421–1430.

    • Search Google Scholar
    • Export Citation
  • ScrocchiLA & Drucker DJ 1998 Effects of aging and a high fat diet on body weight and glucose tolerance in glucagon-like peptide-1 receptor −/− mice. Endocrinology1393127–3132.

    • Search Google Scholar
    • Export Citation
  • ScrocchiLA Brown TJ MaClusky N Brubaker PL Auerbach AB Joyner AL & Drucker DJ 1996 Glucose intolerance but normal satiety in mice with a null mutation in the glucagon-like peptide 1 receptor gene. Nature Medicine21254–1258.

    • Search Google Scholar
    • Export Citation
  • StevensJF1971 Determination of glucose by an automatic analyser. Clinica Chimica Acta32199–201.

  • SzaynaM Doyle ME Betkey JA Holloway HW Spencer RG Greig NH & Egan JM 2000 Exendin-4 decelerates food intake weight gain and fat deposition in Zucker rats. Endocrinology1411936–1941.

    • Search Google Scholar
    • Export Citation
  • ThorensB Porret A Buhler L Deng SP Morel P & Widmann C 1993 Cloning and functional expression of the human islet GLP-1 receptor. Demonstration that exendin-4 is an agonist and exendin-(9–39) an antagonist of the receptor. Diabetes421678–1682.

    • Search Google Scholar
    • Export Citation
  • TsengCC Zhang XY & Wolfe MM 1999 Effect of GIP and GLP-1 antagonists on insulin release in the rat. American Journal of Physiology – Endocrinology and Metabolism276E1049–E1054.

    • Search Google Scholar
    • Export Citation
  • TurtonMD O’Shea D Gunn I Beak SA Edwards CM Meeran K Choi SJ Taylor GM Heath MM Lambert PD Wilding JP Smith DM Ghatei MA Herbert J & Bloom SR 1996 A role for glucagon-like peptide-1 in the central regulation of feeding. Nature37969–72.

    • Search Google Scholar
    • Export Citation
  • ValverdeI Morales M Clemente F Lopez-Delgado MI Delgado E Perea A & Villanueva-Peñacarrillo ML 1994 Glucagon-like peptide 1: a potent glycogenic hormone. FEBS Letters349313–316.

    • Search Google Scholar
    • Export Citation
  • Villanueva-PeñacarrilloML Alcantara AI Clemente F Delgado E & Valverde I 1994 Potent glycogenic effect of GLP-1(7–36)amide in rat skeletal muscle. Diabetologia371163–1166.

    • Search Google Scholar
    • Export Citation
  • VilsbollT Krarup T Deacon CF Madsbad S & Holst JJ 2001 Reduced postprandial concentrations of intact biologically active glucagon-like peptide 1 in type 2 diabetic patients. Diabetes50609–613.

    • Search Google Scholar
    • Export Citation
  • VilsbollT Krarup T Sonne J Madsbad S Volund A Juul AG & Holst JJ 2003 Incretin secretion in relation to meal size and body weight in healthy subjects and people with type 1 and type 2 diabetes mellitus. Journal of Clinical Endocrinology and Metabolism882706–2713.

    • Search Google Scholar
    • Export Citation
  • WangZ Wang RM Owji AA Smith DM Ghatei MA & Bloom SR 1995 Glucagon-like peptide-1 is a physiological incretin in rat. Journal of Clinical Investigation95417–421.

    • Search Google Scholar
    • Export Citation
  • YipRG & Wolfe MM 2000 GIP biology and fat metabolism. Life Sciences6691–103.

  • YoungAA Gedulin BR Bhavsar S Bodkin N Jodka C Hansen B & Denaro M 1999 Glucose-lowering and insulin-sensitizing actions of exendin-4. Studies in obese diabetic (ob/obdb/db) mice diabetic fatty Zucker rats and diabetic rhesus monkeys (Macaca mulatto). Diabetes481026–1034.

    • Search Google Scholar
    • Export Citation

If the inline PDF is not rendering correctly, you can download the PDF file here.

 

      Society for Endocrinology

Sept 2018 onwards Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 536 97 9
PDF Downloads 447 122 7
  • View in gallery

    Acute effects of Ex(9–39) on GLP-1-induced glucose lowering and insulin release in ob/ob mice. Concentrations of (A) plasma glucose and (B) insulin prior to, and 15, 30 and 60 min after intraperitoneal administration of glucose alone (18 mmol/l per kg) or in combination with 25 nmol/kg GLP-1, 25 nmol/kg GLP-1 plus equimolar GLP-1 or 25 nmol/kg GLP-1 plus equimolar Ex(9–39). The time of injection is indicated by the arrows. Plasma glucose and plasma insulin AUC values for 0–60 min after injection are shown. Values are means ± s.e.m. for eight mice. *P<0.05, **P<0.01 and ***P<0.001 compared with glucose alone. ΔP<0.05, ΔΔP<0.01 and ΔΔΔP<0.001 compared with GLP-1 plus GLP-1.

  • View in gallery

    Food intake, body weight and plasma glucose and insulin concentrations of ob/ob mice receiving 11 daily injections of either saline or Ex(9–39). (A) Body weight, (B) food intake, (C) plasma glucose and (D) plasma insulin concentrations were measured for 5 days prior to, for 11 days during (indicated by solid bars) and for 9 days after treatment with saline or Ex(9–39) (25 nmol/kg body weight). Values are means ± s.e.m. for eight mice. *P<0.05 compared with saline group.

  • View in gallery

    Food intake, body weight and plasma glucose and insulin concentrations of normal mice receiving 11 daily injections of either saline or Ex(9–39). (A) Body weight, (B) food intake, (C) plasma glucose and (D) plasma insulin concentrations were measured for 5 days prior to, for 11 days during (indicated by solid bars) and for 9 days after treatment with saline or Ex(9–39) (25 nmol/kg body weight). Values are means ± s.e.m. for eight mice.

  • View in gallery

    Long-term effects of Ex(9–39) treatment on glucose and insulin responses to intraperitoneal glucose administration in ob/ob mice. (A) Plasma glucose and (B) plasma insulin concentrations were measured prior to and at intervals after intraperitoneal administration of glucose (18 mmol/kg body weight) after 11 days of treatment with Ex(9–39). The time of injection is indicated by the arrows. Plasma glucose and plasma insulin AUC values for 0–60 min after injection are shown. Values are means ± s.e.m. for eight mice. *P<0.05 compared with saline.

  • View in gallery

    Reversal of long-term effects of Ex(9–39) treatment on glucose and insulin responses to intraperitoneal glucose in ob/ob mice. (A) Plasma glucose and (B) plasma insulin concentrations were measured prior to and at intervals after intraperitoneal administration of glucose (18 mmol/kg body weight) 9 days after cessation of Ex(9–39) treatment. The time of injection is indicated by the arrows. Plasma glucose and plasma insulin AUC values for 0–60 min after injection are shown. Values are means ± s.e.m. for eight mice.

  • View in gallery

    Long-term effects of Ex(9–39) treatment on glucose and insulin responses to intraperitoneal glucose administration in normal mice. (A) Plasma glucose and (B) plasma insulin concentrations were measured prior to and at intervals after intraperitoneal administration of glucose (18 mmol/kg body weight) after 11 days treatment with Ex(9–39). The time of injection is indicated by the arrows. Plasma glucose and plasma insulin AUC values for 0–60 min after injection are shown. Values are means ± s.e.m. for eight mice.

  • View in gallery

    Long-term effects of Ex(9–39) treatment on glucose and insulin responses to feeding in ob/ob mice. Following the 11-day treatment period mice were fasted (18 h) overnight. At 0900 h, free access to food was allowed for 15 min (indicated by the solid bars) and (A) plasma glucose and (B) plasma insulin concentrations were measured. Plasma glucose and plasma insulin AUC values for 0–105 min after feeding are shown. Values are means ± s.e.m. for eight mice.

  • View in gallery

    Long-term effects of Ex(9–39) treatment on glucose and insulin responses to feeding in normal mice. Following the 11-day treatment period mice were fasted (18 h) overnight. At 0900 h, free access to food was allowed for 15 min (indicated by the solid bars) and (A) plasma glucose and (B) plasma insulin concentrations were measured. Plasma glucose and plasma insulin AUC values for 0–105 min after feeding are shown. Values are means ± s.e.m. for eight mice.

  • View in gallery

    Insulin sensitivity of (A) ob/ob mice and (B) normal mice chronically treated for 11 days with Ex(9–39). The time of injection is indicated by the arrows. Plasma glucose concentrations were measured prior to and at intervals after intraperitoneal administration of insulin (50U/kg body weight). Corresponding AUC values (0–60 min) for plasma glucose show overall effects to exogenous insulin administration.

  • AniniY & Brubaker PL 2003 Role of leptin in the regulation of glucagon-like peptide-1 secretion. Diabetes52252–259.

  • BaileyCJ & Flatt PR 1995 Develepment of antidiabetic drugs. In Drugs Diet and Disease: Mechanistic Approaches to Diabetes pp 279–326. Eds C Ioanides & PR Flatt. London: Ellis Horwood.

  • BaileyCJ & Flatt PR 2003 Animal syndromes resembling type 2 diabetes. In Textbook of Diabetes edn 3 pp 25.1–25.30. Eds JC Pickup & G Williams. Oxford: Blackwell Scientific Publications.

  • BaileyCJ Flatt PR & Atkins TW 1982 Influence of genetic background and age on the expression of the obese hyperglycaemic syndrome in Aston ob/ob mice. International Journal of Obesity611–21.

    • Search Google Scholar
    • Export Citation
  • BogardusC Lillioja S Mott DM Hollenbeck C & Reaven G 1985 Relationship between degree of obesity and in vivo insulin action in man. American Journal of Physiology – Endocrinology and Metabolism248E286–E291.

    • Search Google Scholar
    • Export Citation
  • BuringtonRS1973Handbook of Mathematical Tables and Formulas. New York: McGraw-Hill.

  • EdwardsCM Todd JF Mahmoudi M Wang Z Wang RM Ghatei MA & Bloom SR 1999 Glucagon-like peptide 1 has a physiological role in the control of postprandial glucose in humans: studies with the antagonist exendin 9–39. Diabetes4886–93.

    • Search Google Scholar
    • Export Citation
  • ElahiD Clocquet A & Egan JM 1999 Exendin-4 is insulinotropic in non-diabetic and diabetic subjects. Diabetologia42148A.

  • EngJ Kleinman WA Singh L Singh G & Raufman JP 1992 Isolation and characterization of exendin-4 an exendin-3 analogue from Heloderma suspectum venom. Further evidence for an exendin receptor on dispersed acini from guinea pig pancreas. Journal of Biological Chemistry2677402–7405.

    • Search Google Scholar
    • Export Citation
  • FlamezD Van Breusegem A Scrocchi LA Quartier E Pipeleers D Drucker DJ & Schuit F 1998 Mouse pancreatic beta-cells exhibit preserved glucose competence after disruption of the glucagon-like peptide-1 receptor gene. Diabetes47646–652.

    • Search Google Scholar
    • Export Citation
  • FlattPR & Bailey CJ 1981 Abnormal plasma glucose and insulin responses in heterozygous lean (ob/+) mice. Diabetologia20573–577.

  • FlattPR Bailey CJ Kwasowski P Swanston-Flatt SK & Marks V 1983 Abnormalities of GIP in spontaneous syndromes of obesity and diabetes in mice. Diabetes32433–435.

    • Search Google Scholar
    • Export Citation
  • FlattPR Bailey CJ Kwasowski P Page P & Marks V 1984 Plasma immunoreactive gastric inhibitory polypeptide in obese hyperglycaemic (ob/ob) mice. Journal of Endocrinology101249–256.

    • Search Google Scholar
    • Export Citation
  • FlintA Raben A Ersboll AK Holst JJ & Astrup A 2001 The effect of physiological levels of glucagon-like peptide-1 on appetite gastric emptying energy and substrate metabolism in obesity. International Journal of Obesity and Related Metabolic Disorders25781–792.

    • Search Google Scholar
    • Export Citation
  • GaultVA Flatt CJ Harriott P Green BD & O’Harte FPM 2003 Effects of the novel (Pro3)GIP antagonist and exendin (9–39) amide GIP and GLP-1 induced cyclic AMP generation insulin secretion and postprandial insulin release in obese diabetic (ob/ob) mice: evidence that GIP is the major physiological incretin. Diabetologia46222–230.

    • Search Google Scholar
    • Export Citation
  • GökeR Fehmann HC Linn T Schmidt H Krause M Eng J & Göke B 1993 Exendin-4 is a high potency agonist and truncated exendin-(9–39)-amide an antagonist at the glucagon-like peptide 1-(7–36)-amide receptor of insulin-secreting beta-cells. Journal of Biological Chemistry26819650–19655.

    • Search Google Scholar
    • Export Citation
  • GolayA & Felber JP 1994 Evolution from obesity to diabetes. Diabetes Metabolism203–14.

  • GreenBD Mooney MH Gault VA Irwin N Bailey CJ Harriott P Greer B Flatt PR & O’Harte FPM 2004 Lys9 for Glu9 substitution in glucagon-like peptide-1(7–36)amide (GLP-1) confers DPP IV resistance with cellular and metabolic actions similar to those of established antagonists GLP-1(9–36)amide and exendin (9–39). Metabolism53252–259.

    • Search Google Scholar
    • Export Citation
  • GreigNH Holloway HW De Ore KA Jani D Wang Y Zhou J Garant MJ & Egan JM 1999 Once daily injection of exendin-4 to diabetic mice achieves long-term beneficial effects on blood glucose concentrations. Diabetologia4245–50.

    • Search Google Scholar
    • Export Citation
  • HolzGG & Chepurny OG 2003 Glucagon-like peptide-1 synthetic analogs: new therapeutic agents for use in the treatment of diabetes mellitus. Current Medicinal Chemistry102471–2483.

    • Search Google Scholar
    • Export Citation
  • KolligsF Fehmann HC Göke R & Göke B 1995 Reduction of the incretin effect in rats by the glucagon-like peptide 1 receptor antagonist exendin (9–39) amide. Diabetes4416–19.

    • Search Google Scholar
    • Export Citation
  • KoltermanOG Gray RS Griffin J Burstein P Insel J Scarlett JA & Olefsky JM 1981 Receptor and postreceptor defects contribute to the insulin resistance in non-insulin-dependent diabetes mellitus. Journal of Clinical Investigation68957–969.

    • Search Google Scholar
    • Export Citation
  • LarsenPJ Fledelius C Knudsen LB & Tang-Christensen M 2001 Systemic administration of the long-acting GLP-1 derivative NN2211 induces lasting and reversible weight loss in both normal and obese rats. Diabetes502530–2539.

    • Search Google Scholar
    • Export Citation
  • MannucciE Ognibene A Cremasco F Bardini G Mencucci A Pierazzuoli E Ciani S Fanelli A Messeri G & Rotella CM 2000 Glucagon-like peptide (GLP)-1 and leptin concentrations in obese patients with Type 2 diabetes mellitus. Diabetic Medicine10713–719.

    • Search Google Scholar
    • Export Citation
  • MooneyMH Abdel-Wahab YHA McKillop AM O’Harte FPM & Flatt PR 2002 Evaluation of glycated glucagon-like peptide-1(7–36)amide in intestinal tissues of normal and diabetic animal models. Biochimica et Biophysica Acta156975–80.

    • Search Google Scholar
    • Export Citation
  • O’HarteFPM Gray AM Abdel-Wahab YHA & Flatt PR 1997 Effects of non-glycated and glycated glucagon-like peptide-1(7–36) amide on glucose metabolism in isolated mouse abdominal muscle. Peptides181327–1333.

    • Search Google Scholar
    • Export Citation
  • PedersonRA Satkunarajah M McIntosh CH Scrocchi LA Flamez D Schuit F Drucker DJ & Wheeler MB 1998 Enhanced glucose-dependent insulinotropic polypeptide secretion and insulinotropic action in glucagon-like peptide 1 receptor −/− mice. Diabetes471046–1052.

    • Search Google Scholar
    • Export Citation
  • RanganathLR Beety JM Morgan LM Wright JW Howland R & Marks V 1996 Attenuated GLP-1 secretion in obesity: cause or consequence? Gut38916–919.

    • Search Google Scholar
    • Export Citation
  • RuterJ Hoffmann T Demuth HU Moschansky P Klapp BF & Hildebrandt M 2004 Evidence for an interaction between leptin T cell costimulatory antigens CD28 CTLA-4 and CD26 (dipeptidyl peptidase IV) in BCG-induced immune responses of leptin- and leptin receptor-deficient mice. Biological Chemistry385537–541.

    • Search Google Scholar
    • Export Citation
  • SchickRR Zimmermann JP vorm Walde T & Schusdziarra V 2003 Peptides that regulate food intake: glucagon-like peptide 1-(7–36) amide acts at lateral and medial hypothalamic sites to suppress feeding in rats. American Journal of Physiology – Regulatory Integrative and Comparative Physiology284R1427–R1435.

    • Search Google Scholar
    • Export Citation
  • SchirraJ Sturm K Leicht P Arnold R Göke B & Katschinski M 1998 Exendin(9–39)amide is an antagonist of glucagon-like peptide-1(7–36)amide in humans. Journal of Clinical Investigation1011421–1430.

    • Search Google Scholar
    • Export Citation
  • ScrocchiLA & Drucker DJ 1998 Effects of aging and a high fat diet on body weight and glucose tolerance in glucagon-like peptide-1 receptor −/− mice. Endocrinology1393127–3132.

    • Search Google Scholar
    • Export Citation
  • ScrocchiLA Brown TJ MaClusky N Brubaker PL Auerbach AB Joyner AL & Drucker DJ 1996 Glucose intolerance but normal satiety in mice with a null mutation in the glucagon-like peptide 1 receptor gene. Nature Medicine21254–1258.

    • Search Google Scholar
    • Export Citation
  • StevensJF1971 Determination of glucose by an automatic analyser. Clinica Chimica Acta32199–201.

  • SzaynaM Doyle ME Betkey JA Holloway HW Spencer RG Greig NH & Egan JM 2000 Exendin-4 decelerates food intake weight gain and fat deposition in Zucker rats. Endocrinology1411936–1941.

    • Search Google Scholar
    • Export Citation
  • ThorensB Porret A Buhler L Deng SP Morel P & Widmann C 1993 Cloning and functional expression of the human islet GLP-1 receptor. Demonstration that exendin-4 is an agonist and exendin-(9–39) an antagonist of the receptor. Diabetes421678–1682.

    • Search Google Scholar
    • Export Citation
  • TsengCC Zhang XY & Wolfe MM 1999 Effect of GIP and GLP-1 antagonists on insulin release in the rat. American Journal of Physiology – Endocrinology and Metabolism276E1049–E1054.

    • Search Google Scholar
    • Export Citation
  • TurtonMD O’Shea D Gunn I Beak SA Edwards CM Meeran K Choi SJ Taylor GM Heath MM Lambert PD Wilding JP Smith DM Ghatei MA Herbert J & Bloom SR 1996 A role for glucagon-like peptide-1 in the central regulation of feeding. Nature37969–72.

    • Search Google Scholar
    • Export Citation
  • ValverdeI Morales M Clemente F Lopez-Delgado MI Delgado E Perea A & Villanueva-Peñacarrillo ML 1994 Glucagon-like peptide 1: a potent glycogenic hormone. FEBS Letters349313–316.

    • Search Google Scholar
    • Export Citation
  • Villanueva-PeñacarrilloML Alcantara AI Clemente F Delgado E & Valverde I 1994 Potent glycogenic effect of GLP-1(7–36)amide in rat skeletal muscle. Diabetologia371163–1166.

    • Search Google Scholar
    • Export Citation
  • VilsbollT Krarup T Deacon CF Madsbad S & Holst JJ 2001 Reduced postprandial concentrations of intact biologically active glucagon-like peptide 1 in type 2 diabetic patients. Diabetes50609–613.

    • Search Google Scholar
    • Export Citation
  • VilsbollT Krarup T Sonne J Madsbad S Volund A Juul AG & Holst JJ 2003 Incretin secretion in relation to meal size and body weight in healthy subjects and people with type 1 and type 2 diabetes mellitus. Journal of Clinical Endocrinology and Metabolism882706–2713.

    • Search Google Scholar
    • Export Citation
  • WangZ Wang RM Owji AA Smith DM Ghatei MA & Bloom SR 1995 Glucagon-like peptide-1 is a physiological incretin in rat. Journal of Clinical Investigation95417–421.

    • Search Google Scholar
    • Export Citation
  • YipRG & Wolfe MM 2000 GIP biology and fat metabolism. Life Sciences6691–103.

  • YoungAA Gedulin BR Bhavsar S Bodkin N Jodka C Hansen B & Denaro M 1999 Glucose-lowering and insulin-sensitizing actions of exendin-4. Studies in obese diabetic (ob/obdb/db) mice diabetic fatty Zucker rats and diabetic rhesus monkeys (Macaca mulatto). Diabetes481026–1034.

    • Search Google Scholar
    • Export Citation