GPR91, also known as SUCNR1, is a G Protein-Coupled Receptor with 339 amino acids. It has been characterized as a receptor for Succinate, a citric acid cycle intermediate. Succinate plays a key role in energy metabolism. Local interstitial accumulation of Succinate has recently been reported to serve as an indicator of ischemic or diabetic organ damage in the brain, liver, and kidney. In diabetes patients, the accumulation of Succinate is detectable in the plasma, and more significantly in the renal tubular fluid and urine. It is therefore considered a potential new biomarker of local tissue damage. It has also been shown that Succinate increases blood pressure in animals. The Succinate-induced hypertensive effect involves the renin-angiotensin system that is shown to be absent in GPR91-deficient mice. There is a possible role for GPR91 in renovascular hypertension, a disease closely linked to atherosclerosis, diabetes and renal failure. In a recombinant system overexpressing GPR91, Succinate was shown to not only stimulate calcium mobilization and inositol phosphate (IP) accumulation through the stimulation of Galphaq pathway but also to activate the Erk1/2 MAPK pathway and inhibit forskolin-stimulated cAMP accumulation through Galphai pathway.