GLP-1 is a proglucagon-derived peptide hormone secreted primarily by intestinal L cells during feeding. Its major physiological function is stimulation of pancreatic β-cells to release appropriate amounts of insulin after glucose absorption. Other biological actions exhibited by GLP-1 include suppression of plasma glucagons levels, inhibition of gastric motility, and promotion of satiety. The secretion of GLP-1 from intestinal L cells is stimulated by nutrients, hormones, and neural inputs. On the other hand, insulin has been reported to inhibit GLP-1 release, indicating that a feedback loop mechanism regulates GLP-1 secretion. In addition to being the precursor of GLP-1, proglucagon, whose primary structure is highly conserved in mammalian species, is also the precursor for other members of the glucagon family of peptide hormones including glicentin-related pancreatic peptide (GRPP), glucagons, and GLP-2. Recombinant human GLP-1 is a 3.3 kDa consisting of 31 amino acid residues.