Definition
A 42-residue incretin hormone from intestinal K cells; its receptor is a target of dual and triple agonists.
Glucose-dependent insulinotropic polypeptide is a 42-amino-acid incretin hormone secreted by K cells in the upper small intestine after nutrient intake. Together with GLP-1 it accounts for the incretin effect, the greater insulin response to oral than to intravenous glucose. GIP receptors are expressed in pancreatic islets, adipose tissue and the brain. Tirzepatide, built on a GIP-based sequence, activates both GIP and GLP-1 receptors, and retatrutide adds glucagon receptor activity. The role of the GIP receptor in combination with GLP-1 agonism is still being characterised: GIPR agonism and GIPR antagonism are both under clinical investigation in separate programmes.