In addition, expression levels of the histamine receptors H1R and H2R in intestinal tissue samples from IBS patients are upregulated [84], while administration of antagonists for histamine receptor H1R have been reported to improve abdominal pain in IBS patients as well as hypersensitivity in animal models of IBS through the transient receptor potential vanilloid 1 (TRPV1) [79]. Here, HRH2 is linked to irritable bowel syndrome.