Mucosal mast cell counts correlate with visceral hypersensitivity in patients with diarrhea predominant irritable bowel syndrome

Background and Aim: Although increased mast cells in the gut and their role in visceral hypersensitivity in irritable bowel syndrome have been postulated, this relationship remains unclear. Our aim was to determine whether a relationship exists between the number of mucosal mast cells in the gut and visceral hypersensitivity. Method: Eighteen patients with diarrhea predominant irritable bowel syndrome (D-IBS) (eight females, 10 males aged 25-65 years; mean 42.6 years) with symptoms meeting the Rome-II criteria, and 15 healthy controls (five females, 10 males aged 31-57 years; mean 41.4 years) were recruited. Participants completed a questionnaire for bowel symptoms and psychological distress. Colonic mucosal mast cells were identified immunohistochemically and quantified by image analysis, and maximally tolerable pressures were evaluated using barostat test. Results: Numbers of mast cells were significantly greater in the terminal ileum, ascending colon and rectum of D-IBS patients compared with controls (P < 0.01). A multivariate analysis of the barostat test showed that maximally tolerable pressures of D-IBS patients were significantly lower than those of controls (P < 0.01). When patients were divided into the rectal hypersensitivity (+) and (-) groups by the distension level of 34 mmHg, mast cell counts were significantly higher in the rectal hypersensitivity (-) group than in the rectal hypersensitivity (+) group for the terminal ileum, ascending colon and rectum (P < 0.05, respectively). Conclusions: Rectal sensitivity was enhanced in D-IBS patients with moderately increased mucosal mast cells, but it was attenuated in patients with markedly increased ones. This study might provide evidence for an important role of mast cells in visceral hypersensitivity.