In type-2 diabetes, the overall incretin effect is reduced. 17-36 amidel dose-dependently augmented insulin secretion (insulin, C-peptide) in both groups (P < 0.05). With GIP, the maximum effect in type-2 diabetic patients was significantly lower (by 54%; P < 0.05) than in normal subjects. With GLP-1 17-36 amidel type-2 diabetic patients reached 71% of the increments in C-peptide of normal subjects (difference not significant). Glucagon was lowered during hyperglycemic clamps in normal subjects, but not in type-2 diabetic patients, and further by GLP-1 17-36 amidel in both groups (P < 0.05), but not by GIP. In conclusion, in mild type-2 diabetes, GLP-1 17-36 amidel, in contrast to GIP, retains much of its insulinotropic activity. It also lowers glucagon concentrations. (J. Clin. Invest. 1993. 91:301-307.) Key words: enteroinsular axis* gastric inhibitory peptide -glucagon-like peptide 1 17-36 amidel * hyperglycemic clamp * incretin hormones -pancreatic glucagon

Glucagon-like peptide 1 (GLP-1) (7-36 amide) is a physiological incretin hormone that is released after nutrient intake from the lower gut and stimulates insulin secretion at elevated plasma glucose concentrations. Previous work has shown that even in Type 2 (non-insulin-dependent) diabetic patients GLP-1 (7-36 amide) retains much of its insulinotropic action. However, it is not known whether the magnitude of this response is sufficient to normalize plasma glucose in Type 2 diabetic patients with poor metabolic control. Therefore, in 10 Type 2 diabetic patients with unsatisfactory metabolic control (HbA1c 11.6 +/- 1.7%) on diet and sulphonylurea therapy (in some patients supplemented by metformin or acarbose), 1.2 pmol x kg-1 x min-1 GLP-1 (7-36 amide) or placebo was infused intravenously in the fasting state (plasma glucose 13.1 +/- 0.6 mmol/l). In all patients, insulin (by 17.4 +/- 4.7 nmol x 1-1 x min; p = 0.0157) and C-peptide (by 228.0 +/- 39.1 nmol x 1-1 x min; p = 0.0019) increased significantly over basal levels, glucagon was reduced (by -1418 +/- 308 pmol x 1-1 x min) and plasma glucose reached normal fasting concentrations (4.9 +/- 0.3 mmol/l) within 4 h of GLP-1 (7-36 amide) administration, but not with placebo. When normal fasting plasma glucose concentrations were reached insulin returned towards basal levels and plasma glucose concentrations remained stable despite the ongoing infusion of GLP-1 (7-36 amide). Therefore, exogenous GLP-1 (7-36 amide) is an effective means of normalizing fasting plasma glucose concentrations in poorly-controlled Type 2 diabetic patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Glucagon-like peptide 1 (GLP-1) analogs are increasingly being used in the treatment of type 2 diabetes. It is clear that these drugs lower blood glucose through an increase in insulin secretion and a lowering of glucagon secretion; in addition, they lower body weight and systolic blood pressure and increase heart rate. Using a new monoclonal antibody for immunohistochemistry, we detected GLP-1 receptor (GLP-1R) in important target organs in humans and monkeys. In the pancreas, GLP-1R was predominantly localized in β-cells with a markedly weaker expression in acinar cells. Pancreatic ductal epithelial cells did not express GLP-1R. In the kidney and lung, GLP-1R was exclusively expressed in smooth muscle cells in the walls of arteries and arterioles. In the heart, GLP-1R was localized in myocytes of the sinoatrial node. In the gastrointestinal tract, the highest GLP-1R expression was seen in the Brunner's gland in the duodenum, with lower level expression in parietal cells and smooth muscle cells in the muscularis externa in the stomach and in myenteric plexus neurons throughout the gut. No GLP-1R was seen in primate liver and thyroid. GLP-1R expression seen with immunohistochemistry was confirmed by functional expression using in situ ligand binding with (125)I-GLP-1. In conclusion, these results give important new insight into the molecular mode of action of GLP-1 analogs by identifying the exact cellular localization of GLP-1R.

Glucagon-like peptide 1 (GLP-1) has been shown to inhibit gastric emptying of liquid meals in type 2 diabetic patients. It was the aim of the present study to compare the action of physiological and pharmacological doses of intravenous GLP-1-(7—36) amide and GLP-1-(7—37) on gastric emptying in normal volunteers. Nine healthy subjects participated (26 ± 3 yr; body mass index 22.9 ± 1.6 kg/m2; hemoglobin A1C 5.0 ± 0.2%) in five experiments on separate occasions after an overnight fast. A nasogastric tube was positioned for the determination of gastric volume by use of a dye-dilution technique (phenol red). GLP-1-(7—36) amide (0.4, 0.8, or 1.2 pmol ⋅ kg−1 ⋅ min−1), GLP-1-(7—37) (1.2 pmol ⋅ kg−1 ⋅ min−1), or placebo was infused intravenously from −30 to 240 min. A liquid meal (50 g sucrose, 8% amino acids, 440 ml, 327 kcal) was administered at 0 min. Glucose, insulin, and C-peptide were measured over 240 min. Gastric emptying was dose dependently slowed by GLP-1-(7—36) amide ( P < 0.0001). Effects of GLP-1-(7—37) at 1.2 pmol ⋅ kg−1 ⋅ min−1were virtually identical. GLP-1 dose dependently stimulated fasting insulin secretion (−30 to 0 min) and slightly reduced glucose concentrations. After the meal (0–240 min), integrated incremental glucose ( P < 0.0001) and insulin responses ( P = 0.01) were reduced (dose dependently) rather than enhanced. In conclusion, 1) GLP-1-(7—36) amide or -(7—37) inhibits gastric emptying also in normal subjects, 2) physiological doses (0.4 pmol ⋅ kg−1 ⋅ min−1) still have a significant effect, 3) despite the known insulinotropic actions of GLP-1-(7—36) amide and -(7—37), the net effect of administering GLP-1 with a meal is no change or a reduction in meal-related insulin responses. These findings suggest a primarily inhibitory function for GLP-1 (ileal brake mechanisms).

GLIP has an antidiabetogenic effect, and it may therefore be useful in the treatment of patients with NIDDM:

Using specific radioimmunoassays, we studied the occurrence of amidated and glycine-extended glucagon-like peptide I (GLP-I) molecules in the human small intestine and pancreas and in the circulation system in response to a breakfast meal. Through gel permeation chromatography of extracts of the human pancreas (n = 5), we found that 71% of the GLP-I immunoreactivity eluted as a large molecule corresponding to the major proglucagon fragment, 24% corresponded to GLP-I 1-36 amide, and 5% to GLP-I 1-37. By gel permeation chromatography of extracts of human small intestine (n = 6), we found that all immunoreactivity eluted in one peak at the common elution position of the two insulin-releasing peptides, GLP-I 7-36 amide and GLP-I 7-37. Of the GLP-I immunoreactivity, 80% corresponded to GLP-I 7-36 amide and 20% to GLP-I 7-37. The mean concentrations of amidated GLP-I and glycine-extended GLP-I in fasting plasma were 7 +/- 1 and 6 +/- 1 pM, respectively (n = 6). In response to a breakfast meal, the concentration of amidated GLP-I rose significantly amounting to 41 +/- 5 pM 90 min after the meal ingestion, whereas the concentration of glycine-extended GLP-I only rose slightly to a maximum of 10 +/- 1 pM. Thus, both amidated and glycine-extended GLP-I molecules are produced in the small intestine and in the pancreas in humans. Both amidated and glycine-extended GLP-I are measurable in fasting plasma.(ABSTRACT TRUNCATED AT 250 WORDS)

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By hydrophobic gel permeation and high pressure liquid chromatography we isolated from pig intestinal mucosa a peptide which corresponds to proglucagon 78–107 as suggested by chromatography and determination of its N‐terminal sequence. Natural and synthetic proglucagon 78–107 dose dependently and potently increased insulin secretion from the isolated perfused pig pancreas. Proglucagon 78–107 also secreted by the small intestine may participate in the hormonal control of insulin secretion.