Incretin hormones are intestinally derived hormones stimulating glucose-dependent insulin secretion in response to food intake. Incretin hormones play an important role in glucose homeostasis.
The first incretin hormone identified was gastric inhibitory polypeptide (GIP), which is also referred to as glucose-dependent insulinotropic polypeptide. In the early 1980s, glucagon-like peptide (GLP‑1) was discovered as a proglucagon cleavage product produced in intestinal L cells.
GLP-1 is an incretin hormone with multiple glucoregulatory actions, including enhancement of glucose-dependent insulin secretion, suppression of inappropriately elevated glucagon secretion, slowing of gastric emptying, and reduction of food intake and body weight. Postprandial secretion of GLP-1 is reduced in patients with type 2 diabetes, suggesting that the GLP-1 signaling pathway is an attractive therapeutic target. However, GLP-1 is rapidly degraded by the enzyme dipeptidyl peptidase-IV and has a relatively short half-life.
The therapeutic potential of the GLP-1 pathway has led to the development of a class of compounds that share several glucoregulatory actions with GLP-1 but are resistant to dipeptidyl peptidase-IV degradation.
GLP-1 receptor agonists provide significant improvements in HbA1c, and this class of drugs also helps to decrease the risk of hypoglycaemia and promote weight loss. Individual GLP-1 receptor agonists have widely differing pharmacokinetic and pharmacodynamic profiles. Shorter-acting GLP-1 receptor agonists appear to have a marked effect on postprandial glucose levels, which is likely due to substantial slowing of gastric emptying, whereas longer-acting GLP-1 receptor agonists affect mainly fasting glucose and do not have any notable long term effect on gastric emptying.