The citric acid cycle intermediates receptor family contains both succinate and oxoglutarate receptors, known as GPR91 and GPR99 respectively. In 2004, the endogenous ligand for GPR91 was discovered. Since then, GPR91 has undergone research to identify its role in inflammation, retinal angiogenesis, and renin production. The oxoglutarate receptor is found in tissues such as the trachea, salivary glands, and nasal mucosa, playing a large role in allergic reactions. Antagonists for GPR99 can be used for the treatment of asthma, allergic rhinitis, bronchoconstriction, primary dysmenorrhoea, and urticaria.