Gastric inhibitory polypeptide

Gastric inhibitory polypeptide (GIP), also known as glucose-dependent insulinotropic polypeptide is an inhibiting hormone of the secretin family of hormones.^[5] While it is a weak inhibitor of gastric acid secretion, its main role, being an incretin, is to stimulate insulin secretion.^[6]

GIP, along with glucagon-like peptide-1 (GLP-1), belongs to a class of molecules referred to as incretins,^[7] which stimulate insulin release on oral food intake.

Synthesis and transport

GIP is derived from a 153-amino acid proprotein encoded by the GIP gene and circulates as a biologically active 42-amino acid peptide. It is synthesized by K cells, which are found in the

In addition to its role as an incretin, GIP is known to inhibit apoptosis of the pancreatic beta cells and to promote their proliferation. It also stimulates glucagon secretion and fat accumulation. GIP receptors are expressed in many organs and tissues including the central nervous system enabling GIP to influence hippocampal memory formation and regulation of appetite and satiety.^[13]

GIP recently appeared as a major player in bone remodeling. Researchers at Universities of Angers and Ulster evidenced that genetic ablation of the GIP receptor in mice resulted in profound alterations of bone microarchitecture through modification of the adipokine network.^[14] Furthermore, the deficiency in GIP receptors has also been associated in mice with a dramatic decrease in bone quality and a subsequent increase in fracture risk.^[15] However, the results obtained by these groups are far from conclusive because their animal models give discordant answers and these works should be analysed very carefully.^{[citation needed]}

Pathology

It has been found that