| Objective: To determine the numbers of mast cell and the content of tryptase in the ascending colon mucus in patients with diarrhea-predominant irritable bowel syndrome (IBS-D), to investigate the effect of tryptase on the visceral sensitivity and the expressions of substance P(SP), calcitonin gene-related peptide(CGRP) on cornu dorsale medullae spinalis in mince, and then to explore the roles of tryptase in the pathogenesis of IBS-D.Methods: Twenty-four patients with IBS-D and 12 healthy volunteers were included in this study. The mucosal biopsies were collected from ascending colon during colonoscopy, the mucosal mast cells were detected by toluidine blue stains, and the concentration of tryptase in biopsy-cultured supernatants was detected by ELISA.The relations of mast cell numbers, tryptase level with gastrointestinal symptoms Rating scale(GSRS) in IBS-D were analyzed respectivly.Fifty-six C57BL/6 mice were randomly divided into 7 groups and then were administrated intracolonically with volunteer's biopsy-cultured supernatants (group A), IBS-D patient's biopsy-cultured supernatants (group B) , supernatants of IBS-D biopsy-cocultured with FUT-175(group C), tryptase solution of 0.6ng(group D) and of 2.2ng(group E), tryptase + FUT-175(group F), and 0.9% sodium chloride as control (group G) respectively.The abdominal myoelectric activities (AMAs) during colorectal distension (CRD) were recorded, and the expressions of SP, CGRP in spine cord of these mice were detected by immunohistochemistry.Results: The numbers of mast cells (6.33±1.64 /HPE) in the ascending colon of patients with IBS-D were significantly higher than those in controls (p=0.000). The contents of tryptase (0.072±0.023ng/mg) from IBS-D patient's biopsies were significantly higher than those in controls (p=0.000). A positive correlation was detected between the content of tryptase and the GSRS (r=0.581, p=0.003). However, there was not a correlation neither between the mast cell numbers and the tryptase contents (r=0.010,p=0.963), nor between the mast cell numbers and the GSRS (r=0.209, p =0.326).The AMAs in group B (27.50±5.23, 41.69±5.80, 54.03±6.13uV) and E (27.05±1.66, 40.66±3.39, 54.38±4.68 uV) with colonic distention by 30, 45, 60mmHg were significantly higher than those in group A (22.49±3.43, 31.45±3.62, 47.68±5.78uV), group C (23.45±2.81, 34.40±3.70,44.81±6.62uV), group D (22.92±3.31, 33.81±3.73,45.73±6.16 uV), group F (20.94±3.17, 34.08±4.67, 43.02±4.34uV) and group G (22.24±3.49, 32.67±6.99, 47.82±6.79 uV) respectively (p<0.05). The SP and CGRP average integrated option density(IOD) in group B (121.72±4.67, 123.54±4.32) and E (124.69±5.06, 126.32±5.09) were higher than in group A (114.76±3.02,105.79±5.22), group C (113.62±4.04, 110.06±4.89), group D (115.75±3.99, 106.93±4.85), group F (112.04±5.92, 107.79±5.43), group G (114.74±3.90, 110.59±4.63) respectively (p﹤0.05). There was no significant difference between group B and group E, and there was no significant difference among group A, C, D, F and group G.Conclusion: These results demonstrated that the increasing mast cell numbers and the abundant tryptase in the colon mucousa may be involved in the pathogenesis of IBS-D. Tryptase could stimulate the expressions of SP, CGRP in spine cord, which may alter the visceral sensitivity.
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