text: Fig.1: During a meal, the incretins glucagon-like peptide 1 (GLP-1) and glucose-dependent gastric inhibitory polypeptide (GIP) are released by the small intestine into the blood stream. These hormones regulate insulin secretion in a glucose-dependent manner. (GLP-1 has many roles in the human body. It stimulates insulin biosynthesis, inhibits glucagon secretion, slows gastric emptying, reduces appetite and stimulates regeneration of islet β-cells.)
  GLP-1 and GIP have extremely short plasma half-lives due to very rapid inactivation, catalyzed by the enzyme DPP-4. Inhibition of DPP-4 slows their inactivation, thereby potentiating their action, leading to lower plasma glucose levels, hence its utility in the treatment of type 2 diabetes. (Figure 1).