http://www.gastrosource.com/frameset_GI_NEW.asp8 Dec 2005 Increased histamine receptor expression in IBS Gut 2005; Early online publication German researchers have discovered that patients with irritable bowel syndrome (IBS) and food allergies (FA) show increased expression of the histamine receptors (HRs) H1R and H2R.These findings emerge from the first examination of its kind of the expression and distribution of HRs in humans, which also indicated that H1R, H2R, and H4R are located along the course of the human gastrointestinal (GI) tract.Stephan Bischoff, from the University of Hohenheim, and collaborators analyzed the expression of H1R, H2R, H3R, and H4R messenger (m)RNA in human GI tissue samples from 33 individuals who underwent bowel resection due to GI cancer, 30 patients with IBS (19 of whom had concomitant intestinal FA), and 14 control individuals who underwent colonoscopy for other reasons.Study results revealed that levels of H1R, H2R, and H4R mRNA were expressed throughout the GI tract in patients with GI cancer and controls, but H3R mRNA was not detected at any location. H1R, H2R, and H4R appeared to be evenly distributed in tissue from the duodenum, ileum, colon, sigma, and rectum.Moreover, analyses of tissues from GI cancer patients and controls showed that H1R and H2R, and, to a lesser degree, H4R, were expressed in epithelial cells, and in the mucosa and muscular layer. The enteric nervous system appeared to be particularly devoid of H3R.Interestingly, patients with IBS and FA had significantly upregulated H1R and H2R levels in comparison with controls, H4R levels were similar to those in controls, and H3R mRNA levels could only be detected in two specimens from IBS and FA patients, indicating that this receptor is not upregulated in people with these conditions.Reporting in an early online publication of the journal Gut, Bischoff et al explain that IBS symptoms may be induced by impaired histamine metabolism. Alternatively, the elevated HR expression found in patients with IBS and FA may cause histamine hypersensitivity, producing IBS-like symptoms.They summarize: "We show that H1R, H2R, and H4R are present in the human GI tract and that the expression of H1R and H2R is upregulated in patients with FA or IBS. In contrast to previous studies in guinea pigs, we conclude that H3R is not expressed in the human intestine."