What is GIP receptor?

The GIP receptor (GIPR) is the receptor for glucose-dependent insulinotropic polypeptide, the incretin released from endocrine cells of the small intestine after a meal. Its cloning in 1993 placed it in the secretin–VIP family of G protein-coupled receptors, now called class B1, alongside the GLP-1 receptor and glucagon receptor ^[1]. The hormone's older name, gastric inhibitory polypeptide, survives in the gene symbol and in much of the pre-2000 literature.

Signalling and distribution

Expressed in cultured cells, the cloned receptor raised cAMP with an EC50 of 0.3 nM and also increased intracellular calcium ^[1]. The same study mapped its mRNA:

The brain signal was a puzzle at the time, because GIP mRNA itself could not be found there ^[1].

The endogenous ligand and its breakdown

GIP is secreted by intestinal K cells and GLP-1 by L cells, and both are degraded rapidly after release, with dipeptidyl peptidase-4 (DPP-4) responsible for the initial inactivation. DPP-4 removes the first two residues of GIP(1-42) to give GIP(3-42), which becomes the major circulating form ^[2]. Resistance to this N-terminal cleavage is therefore a design consideration for incretin analogues and one determinant of their half-life.

Species differences

GIPR pharmacology does not translate cleanly between rodents and humans. In transfected COS-7 cells, human (Pro3)GIP was a full agonist at the human receptor, while the rat and mouse versions were partial agonists at their own receptors; rodent GIPs were also more potent and efficacious at rodent receptors than human GIP ^[3]. A ligand widely used as a GIPR "antagonist" in mouse studies turned out not to antagonise the human receptor at all.

GIPR in multi-agonist research

The last two rows sit awkwardly together. GIPR-knockout mice resist diet-induced obesity, and antagonist antibodies limited body-weight gain in diet-induced obese mice and lowered body weight in obese non-human primates ^[6], yet co-agonist peptides that activate GIPR are studied for the same metabolic endpoints. A 2025 multi-author review credits this apparent agonist–antagonist paradox with much of the renewed interest in GIP biology ^[7].

Points of confusion

• Two names, one hormone. "Gastric inhibitory polypeptide" and "glucose-dependent insulinotropic polypeptide" are the same 42-residue peptide.
• Rodent data need the right ligand. Use species-matched GIP when comparing receptor responses ^[3].
• Balance has to be measured. Multi-receptor agonists can be markedly more active at one receptor than another ^{[4, 5]}; comparing EC50 values at each receptor, in the same assay format, is the fair test. The concentration–response design guide covers how to set that up.