that aim to improve β-cell function and survival. Glucagon-like peptide 1 (GLP-1) is a potent incretin hormone secreted by the intestinal L cells in response to food intake ( Drucker 2001 ). GLP-1 exerts multiple effects on pancreatic β
G Üçkaya, P Delagrange, A Chavanieu, G Grassy, M-F Berthault, A Ktorza, E Cerasi, G Leibowitz and N Kaiser
M L Villanueva-Peñacarrillo, E Delgado, M A Trapote, A Alcántara, F Clemente, M A Luque, A Perea and I Valverde
We have found [125I]glucagon-like peptide (GLP)-1(7–36)amide specific binding activity in rat liver and isolated hepatocyte plasma membranes, with an Mr of approximately 63 000, estimated by cross-linking and SDS-PAGE. The specific binding was time- and membrane protein concentration-dependent, and equally displaced by unlabelled GLP-1(7–36)amide and by GLP-1(1–36)amide, achieving its ID50 at 3×10−9 m of the peptides. GLP-1(7–36)amide did not modify the basal or the glucagon (10−8 m)-stimulated adenylate cyclase in the hepatocyte plasma membranes. These data, together with our previous findings of a potent glycogenic effect of GLP-1(7–36)amide in isolated rat hepatocytes, led us to postulate that the insulin-like effects of this peptide on glucose liver metabolism could be mediated by a type of receptor probably different from that described for GLP-1 in pancreatic B-cells or, alternatively, by the same receptor which, in this tissue as well as in muscle, uses a different transduction system.
Journal of Endocrinology (1995) 146, 183–189
Patricia Vázquez, Isabel Roncero, Enrique Blázquez and Elvira Alvarez
facilitate the action of these proteins involved in the signalling process ( Pawson & Scott 1997 ). The glucagon-like peptide-1 (GLP-1) receptor is a member of the G-protein-coupled receptor subfamily ( Dillon et al. 1993 , Thorens 1993 , Thorens
P. R. Flatt, C. J. Bailey and K. D. Buchanan
This study examines the role of glucagon in the pathogenesis of the obese hyperglycaemic (ob/ob) syndrome in mice. Plasma C-terminal immunoreactive glucagon concentrations were measured in fed and fasted ob/ob mice at different ages between 5–40 weeks, and in 20-week-old mice after the administration of established stimulators and inhibitors of glucagon secretion. Plasma glucagon concentrations were inappropriately raised irrespective of age, nutritional status and the accompanying prominent changes in plasma glucose and insulin concentrations. Glucose suppressed plasma glucagon in the fed but not the fasted state, suggesting a dependence on the marked hyperinsulinaemia associated with feeding. Administration of 0·25 units insulin/kg to fasted mice failed to affect plasma glucagon and glucose concentrations. Increasing the dose to 100 units/kg restored the normal suppressive actions of insulin. Fasted mice showed an exaggerated glucagon response to arginine but not to the parasympathomimetic agent pilocarpine. Fed mice displayed normal plasma glucagon responses to the sympathomimetic agents noradrenaline and adrenaline. Administration of insulin antiserum or 2-deoxy-l-glucose raised plasma glucagon concentrations of fed mice. Contrary to the lack of suppression by glucose in the fasted state, heparin-induced increase in free fatty acids reduced plasma glucagon concentrations. This study demonstrates inappropriate hyperglucagonaemia and defective A-cell function in ob/ob mice. The extent of the abnormality is exacerbated by fasting and appears to result from insensitivity of the A-cell to the normal suppressive action of insulin.
K K Sidhu, R C Fowkes, R H Skelly and J M Burrin
Introduction Glucagon-like peptide 1 (GLP-1) is a proglucagon-derived peptide hormone that is synthesized and secreted by intestinal L-cells in response to the ingestion of nutrients and circulates to the pancreas where it stimulates
I Navarro and T W Moon
We have characterized the specific binding of glucagon in hepatocytes isolated from two teleost species, the American eel (Anguilla rostrata) and the brown bullhead (Ictalurus nebulosus). Specific glucagon binding was 9·3 and 10·7% in bullhead and eel hepatocytes respectively, after a 2-h incubation at 12 °C. Curvilinear Scatchard plots suggest the presence of two classes of binding sites with apparent dissociation constants (K d) of 1·97 nm (high affinity) and 17·3 nm (low affinity) for bullhead and 2·68 and 22·9 nm for eel cells. The number of high-affinity binding sites per cell was significantly higher in the eel (10 413) than in the bullhead (3811). The number of high-affinity insulin-binding sites was approximately two times higher than that for glucagon in bullheads and the opposite in the eel hepatocytes. In competition experiments, insulin did not displace 125I-labelled glucagon binding in the hepatocytes of either species, while glucagon-like peptide-1(7–37) (GLP-1) displaced glucagon but only at high concentrations, suggesting separate glucagon- and GLP-1-binding sites. The rate of dissociation of hepatocyte-bound 125I-labelled glucagon was similar for both species. Preincubation of hepatocytes in 100 nm glucagon decreased the number of high-affinity glucagon-binding sites by approximately 55% in both species, while the K d values remained unchanged. Glucagon bound to the cell surface is internalized by fish hepatocytes. These properties indicate that the glucagon binding to hepatocytes of these two teleost species is similar to that reported for mammalian hepatocytes.
Journal of Endocrinology (1994) 140, 217–227
Colin W Hay, Elaine M Sinclair, Giovanna Bermano, Elaine Durward, Mohammad Tadayyon and Kevin Docherty
Introduction Glucagon-like peptide-1 (GLP-1) is a peptide hormone secreted by the enteroendocrine L-cells of the small intestine in response to food intake ( Kieffer & Habener 1999 , Drucker 2001 ). GLP-1 plays an important role in
P. J. RANDLE
The uptake of glucose by isolated rat diaphragm is increased in the presence of glucagon preparations (at concentrations of 20–200 μg/ml.). Evidence is produced which appears to show that this effect is due to the presence of insulin in preparations of glucagon. The insulin content of an amorphous preparation of glucagon, assayed with isolated diaphragm, appeared to be of the order of 1% (w/w). In view of this finding, it is suggested that no conclusions can be drawn about a possible effect of glucagon on carbohydrate metabolism in muscle until preparations are available which are entirely free from insulin.
H. Vilhardt, T. Krarup, J. J. Holst and P. Bie
Injections and infusions of oxytocin into conscious dogs caused an increase in plasma concentrations of glucose, insulin and glucagon. When blood glucose was clamped at a raised level the injection of oxytocin still increased insulin and glucagon concentrations in plasma. Infusion of somatostatin suppressed plasma concentrations of glucagon and insulin but did not prevent oxytocin-induced increments in blood glucose. Injection of oxytocin still caused a marked release of glucagon, whereas the insulin response was greatly diminished. When endogenous insulin and glucagon secretion was suppressed by infusion of somatostatin and glucose levels were stabilized by concomitant infusions of glucagon and insulin, injections of oxytocin did not alter blood glucose concentrations. It is concluded that the increase in blood glucose following the administration of oxytocin is secondary to the release of glucagon and that oxytocin exerts a direct stimulatory effect on glucagon and possibly insulin secretion.
J. Endocr. (1986) 108, 293–298
R H Rao
The effect of glucagon on ACTH secretion was studied in anaesthetized rats injected with either saline (0·1 ml i.m.) or glucagon (0·02 mg/kg i.m.). For the first 90 min after glucagon injection, plasma ACTH fell by 50% from the basal value of 23 ±4 pmol/l (mean ± s.e.m.) to 11 ±2 (P=0·011), after which an abrupt return to baseline occurred (120 min value: 26 ± 2 pmol/l). In saline injected rats, the baseline ACTH value was not significantly different from either the 90 min value or the 120 min value (27 ±3 vs 21 ± 4 and 24 ± 3 pmol/l respectively; P>0·10). Plasma glucose after glucagon peaked at 11·6 ± 1·1 mmol/l by 15 min but subsequently fell rapidly, attaining the baseline by 60 min. Insulin levels increased sharply after glucagon, from 381 ±78 pmol/l to 3172 ±668 pmol/l at 15 min, and plateaued at approximately 1000 pmol/l thereafter. No changes in glucose or insulin were seen in saline injected rats. The magnitude of suppression of ACTH after glucagon was not affected either by sustained hyperinsulinaemia (≃ 1400 pmol/l), induced with continuous glucose infusion to maintain plasma glucose>12 mmol/l, or by pretreatment with the long-acting somatostatin analogue octreotide (50 μg/kg s.c.). However, the return to baseline between 100 and 120 min was prevented both by hyperinsulinaemia induced with sustained hyperglycaemia, and by octreotide. It is postulated that glucagon may inhibit ACTH secretion either by a direct effect on the hypothalamus or indirectly through insulin, which is known to stimulate endogenous somatostatin release.
Journal of Endocrinology (1995) 145, 51–58