Involvement of Pirt /TRPV1 signaling in acupuncture-induced reduction of visceral hypersensitivity in diarrhea-predominant irritable bowel syndrome rats

Abstract

To observe the effect of electroacupuncture (EA) on the expression of Pirt (a regulator of TRPV1) in the dorsal root ganglia (DRG) and transient receptor potential vanilloid 1 (TRPV1, a molecular sensor of noxious heat and capsaicin) in the colonic mucosa in rats suffering from diarrhea-predominant irritable bowel syndrome (IBS-D), so as to explore its mechanisms underlying alleviation of visceral hypersensitivity of IBS-D. Forty SD rats (half male and half female) were randomly assigned to control, model, EA, and medication groups by lottery, with 10 rats in each group. The IBS-D model was established by chronic unpredictable mild stress (CUMS) and gavage of senna soaking fluid. Rats in the EA group received EA (2 Hz/15 Hz,0.1-1 mA) stimulation of unilateral "Tianshu"(ST25), "Zusanli" (ST36), "Sanyinjiao"(SP6) and "Taichong"(LR3) for 15 min once a day for 14 days, and rats of the medication group received intragastric administration of pinave-rium bromide (10 mL/kg, 2.7 mg/mL) once daily for 14 days. The visceral pain threshold (VPT) was measured by using abdominal wall withdrawal reflex (AWR) test. The diarrhea index （loose stool rate ［total number of loose stool/total number of defecation］ X mean loose degree ［0-4 grades according to the filter paper stain diameter］ in 6 h/d） was used to assess the severity of diarrhea. The expression of Pirt in the DRG and TRPV1 in the colonic mucosa tissue was detected using immunohistochemistry. After modeling, the VPT was obviously reduced (P<0.01), while the diarrhea index, mean optical density of Pirt and TRPV1 were remarkably increased in the model group relevant to the control group (P<0.01). After the interventions, the VPT was obviously increased while the diarrhea index, and the mean optical density of Pirt and TRPV1 was noticeably decreased in both EA and the medicine groups in contrast to the model group (P<0.01). No significant differences were found between the EA and medicine groups in up-regulating VPT and down-regulating the diarrhea index, and Pirt and TRPV1 expression (P>0.05). EA can effectively alleviate visceral hypersensitivity in IBS-D rats, which may be related to its effect in down-regulating the expression level of DRG Pirt and colonic TRPV1.