OBJECTIVETo observe the effect of Tongxie Yaofang (TY) on the number of mast cells (MCs) and the expression of cytokines in rats with visceral hypersensitivity, and to explore roles of TY in treating visceral hypersensitivity and its possible mechanism.

METHODSTotally 30 male adult Sprague Dawley (SD) rats were randomly divided into the blank control group, the model group, and the TY treatment group, 10 in each group. The irritable bowel syndrome (IBS) rat model was established by combining colorectal distention with restraint stress in the TY treatment group and the model group. The visceral hypersensitivity was assessed by abdominal withdrawal reflex (AWR). From the 2nd day of successful modeling, rats in the treatment group were admiministered with TY at the daily dose of 4 g/kg for 4 successive weeks. Equal volume of normal saline was given to rats in the model group for 4 successive weeks. No treatment was given to rats in the blank control group. Four weeks later the number of MCs was counted by using toluidine blue staining. The expression of interleukin-4 (IL-4) and interleukin-9 (IL-9) both in colonic mucosa and serum were measured by enzyme linked immunosorbent assay (ELISA), and the expression of protease-activated receptor type 2 (PAR-2) was detected by Western blot.

RESULTSCompared with the blank control group, the visceral sensitivity was significantly elevated, the number of MCs in the ileocecal junction increased, and the expression of IL-4, IL-9, and PAR-2 in serum and the colonic mucosa significantly increased (P < 0.05). Compared with the model group, the visceral sensitivity significantly decreased, the number of MCs reduced, and the expression of PAR-2 in the colonic mucosa significantly reduced (all P < 0.05), and the expression of IL-4 in colonic mucosa and IL-9 in serum were obviously reduced in the TY treatment group (P < 0.05).

CONCLUSIONTY might improve the visceral hypersensitivity by acting on MCs related cytokines and reducing degranulation of MCs.