Gastric inhibitory polypeptide (GIP) is an inhibiting hormone of the secretin family of hormones. While GIP is a weak inhibitor of gastric acid secretion, its main role is to stimulate insulin secretion – in a glucose-dependent mechanism. Therefore, GIP is referred to as a glucose-dependent insulinotropic peptide.
GIP is derived from a 153-amino acid pro-protein encoded by the GIP gene and circulates as a biologically active 42-amino acid peptide. It is synthesised by K cells, which are found in the mucosa of the duodenum and the jejunum of the gastrointestinal tract. GIP receptors are seven-transmembrane proteins found on beta-cells in the pancreas. These beta-cells are those that are able to simultaneously detect glucose and release insulin as a result to GIP binding.
The clinical relevance of GIP is related to type 2 diabetes mellitus (T2DM); studies have found that T2DM diabetics are unresponsive to GIP and have lower levels of GIP secretion after a meal when compared to non-diabetics. In research involving knockout mice, it was found that absence of the GIP receptors correlates with resistance to obesity.