Electroacupuncture Relieves Visceral Hypersensitivity by Down-regulating Mast Cell Number，PAR-2/TRPV 1 Signaling, etc. in Colonic Tissue of Rats with Irritable Bowel Syndrome

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To observe the effect of electroacupuncture (EA) stimulation of "Shangjuxu" (ST 37, Lower Confluent point) and "Tianshu" (ST 25, Front-Mu point) on visceral pain and expression of colonic tryptase(Try), proteinase-activated receptor 2(PAR-2)，transient receptor potential channel vanilloid subfamily member 1 (TPRV 1)，substance P (SP) and calcitonin gene-related peptide (CGRP) in rats with irritable bowel syndrome (IBS), so as to explore its mechanisms underlying improvement of IBS. Forty male Sprague Dawley rats were equally randomized into normal control (control), model, medication and EA groups (n＝10 in each). The IBS model was established by chronic acute combining stress (CACS, water deprivation, fasting, tail clamping, forced swimming in ice water, restraint, etc.) for 21 days. Rats of the medication group were treated by gavage of Pinaverium Bromide (1 mg/mL, 15 mg/kg), once daily for 14 d. EA (10 Hz/50 Hz, 0.2－0.3 mA) was applied to bilateral ST 37 and ST 25 for 30 min, once daily for 14 d. The muscular withdrawal reflex (AWR) of both abdomen and buttock was detected by colorectal distension (CRD) with a water-filled balloon for examining the visceral hypersensitivity. The number of mast cells in the colonic tissue was counted after toluidine blue stain. The immunoactivity of colonic Try was determined by immunochemistry and the expression of colonic PAR-2, TRVP 1, SP and CGRP proteins detected by Western blot. After modeling, the body weight was significantly decreased in IBS rats of the model, medication and EA groups compared with their own individual pre-treatment and with the control group (P<0.01), and markedly higher in both medication and EA groups than in the model group (P<0.05, P<0.01). The intra-colonic volume thresholds for inducing abdominal and hip AWR were significantly lower in the model group than in the normal control group (P<0.01), and obviously higher in both medication and EA groups than in the model group (P<0.05，P<0.01). The AWR scores of intra-colorectal balloon at volumes of 0.5, 1.0 and 1.5 mL of water were significantly higher in the model group than in the control group (P<0.01), and considerably lower in the EA and medication groups than in the model group (P<0.01). The number of colonic MC and the expression levels of colonic Try, PAR-2, TRPV 1, SP and CGRP proteins were significantly higher in the model group than in the control group (P<0.01), and obviously decreased in both medication and EA groups relevant to the model group (P<0.01). Comparison between the medication and EA groups showed that the decreased expression levels of colonic PAR-2, TRPV 1, SP and CGRP proteins were significantly lower in the EA group than in the medication group (P<0.05), but no significant differences were found between the two groups in intra-colonic volumes for inducing AWR, AWR scores, body weight, and colonic MC number and Try immunoactivity levels (P>0.05)．. EA of ST 37 and ST 25 can relieve visceral hypersensitivity in IBS rats, which may be associated with its effects in down-regulating the number of MC and the expression of PAR-2, TRVP 1, SP, CGRP and Try proteins in the colonic tissue.