Fasting Glucagon-like Peptide-1 Levels Research Articles

Treatment with the Dipeptidyl Peptidase-4 Inhibitor Vildagliptin Improves Fasting Islet-Cell Function in Subjects with Type 2 Diabetes

Dipeptidyl peptidase 4 (DPP-4) inhibitors are proposed to lower blood glucose in type 2 diabetes mellitus (T2DM) by prolonging the activity of the circulating incretins, glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP-1). Consistent with this mechanism of action, DPP-4 inhibitors improve glucose tolerance after meals by increasing insulin and reducing glucagon levels in the plasma. However, DPP-4 inhibitors also reduce fasting blood glucose, an unexpected effect because circulating levels of active GIP and GLP-1 are low in the postabsorptive state. The objective of the study was to examine the effects of DPP-4 inhibition on fasting islet function. We conducted a randomized, double-blind, placebo-controlled trial. The study was performed in General Clinical Research Centers at two University Hospitals. Forty-one subjects with T2DM were treated with metformin or diet, having good glycemic control with glycosylated hemoglobin values of 6.2-7.5%. Subjects were treated with vildagliptin (50 mg twice daily) or placebo for 3 months, followed by a 2-wk washout. Major Outcome Measure: We measured insulin secretion in response to iv glucose and arginine before and after treatment and after drug washout. There were small and comparable reductions in glycosylated hemoglobin in both groups over 3 months. Vildagliptin increased fasting GLP-1 levels in subjects taking metformin, but not those managed with diet, and raised active GIP levels slightly. DPP-4 inhibitor treatment improved the acute insulin and C-peptide responses to glucose (50 and 100% respectively; P < 0.05) and increased the slope of the C-peptide response to glucose (33%; P = 0.023). Vildagliptin improves islet function in T2DM under fasting conditions. This suggests that DPP-4 inhibition has metabolic benefits in addition to enhancing meal-induced GLP-1 and GIP activity.

Effect of hormone therapy on the enteroinsular axis

Menopause is associated with a decline in insulin response to glucose and with insulin resistance. It has been proven that hormone therapy (HT) improves carbohydrate metabolism in postmenopausal women. However, it is known that gastrointestinal hormones play a key role in the coordination of digestion and absorption of ingested nutrients and in the regulation of pancreatic endocrine function. Therefore, the aim of this study was to investigate the effect of HT on gastrointestinal hormones and carbohydrate metabolism in postmenopausal women. The prospective study was performed in 90 healthy postmenopausal women (mean age 54.5 years, standard deviation 3.34 years), of whom 49 completed the study. They were randomized and treated either with continuous transdermal HT (0.05 mg 17[beta]-estradiol every 24 hours) combined with 5 mg oral dydrogesterone daily (group A, n = 25), or with oral HT (2 mg 17[beta]-estradiol semihydrate every 24 hours) combined with 10 mg dydrogesterone as a continuous therapy (group B, n = 8). The control group (group C, n = 16) received no HT. Both basal and meal-stimulated plasma concentrations of glucose, insulin, glucose-dependent insulinotropic peptide (GIP), glucagon-like peptide-1 (GLP-1), and cholecystokinin (CCK), as well as basal estrogen levels, were measured before HT and after 6 and 12 months of treatment. At the same time intervals, all the studied parameters were measured for group C. After 12 months of the transdermal HT, a decrease in both fasting (P < 0.002) and postprandial (P < 0.05) plasma glucose levels was observed. Oral HT reduced only the fasting plasma glucose level in the 12th month of treatment (P < 0.05). Regardless of the route of administration, HT reduced postprandial plasma levels of insulin (oral HT: P < 0.05; transdermal HT: P < 0.02). Fasting plasma levels of GIP were reduced after 6 and 12 months of transdermal HT (P < 0.002 and P < 0.001, respectively). Moreover, levels of postprandial GIP were reduced after 6 and 12 months of transdermal HT (P < 0.002 in both cases). Fasting and postprandial GLP-1 levels were reduced by transdermal HT after 12 months of supplementation. Oral HT also decreased these levels, but not significantly. The observed differences may, however, be related not only to the route of administration, but also to the difference in the dose of estradiol. Regardless of the route of administration, HT did not influence plasma levels of CCK. Hormone therapy significantly influences the enteroinsular axis in postmenopausal women and contributes to the normalization of plasma glucose levels.

Normal Secretion and Action of the Gut Incretin Hormones Glucagon-Like Peptide-1 and Glucose-Dependent Insulinotropic Polypeptide in Young Men with Low Birth Weight

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

Effect of growth hormone on high plasma levels of glucagon-like peptide-1 (GLP-1) in hypophysectomized rats.

Fasting plasma GLP-1 levels were significantly higher in hypophysectomized (hypox) rats (n = 6) than in intact (normal) rats (n = 7) (54.3 +/- 5.2 vs. 33.3 +/- 2.4 pmol/L, p < 0.001). To examine the influence of pituitary hormones on plasma GLP-1 levels, concentrations of plasma glucose, insulin and GLP-1 after an oral glucose load to hypox rats that were given either rat growth hormone (rGH) (n = 7), cortisol and thyroxine (n = 7) or no substitution (n = 6) were compared with those of normal rats (n = 7). Plasma glucose levels in the fasting state and after the glucose ingestion were significantly lower in hypox rats, but the hormonal replacements to hypox rats increased their total glucose levels to those of normal rats, although the increasing patterns were different from those in normal rats. Insulin levels both in the fasting state and after the glucose ingestion were significantly decreased in hypox rats and the fasting and total GLP-1 levels were significantly increased in those rats. rGH substitution significantly increased the total insulin levels in hypox rats and decreased the fasting and total GLP-1 levels closely to levels in normal rats, while substitution with cortisol and thyroxine failed to introduce such a significant effect. These results suggested that secretion of GLP-1 might be influenced by the function of GH.