Effect and Mechanism of Electroacupuncture at ST-36 on Visceral Hypersensitivity in Rats

Background: Visceral hypersensitivity is one of the important pathological mechanisms of irritable bowel syndrome (IBS),and electroacupuncture at ST-36 is gradually used in clinic for treating IBS.However,the effect and mechanism of electroacupuncture at ST-36 on visceral hypersensitivity is still unclear.Aims: To investigate the effect of electroacupuncture at ST-36 on visceral sensitivity and protein expression of mu opioid receptor in proximal colon,distal colon and thalamencephalon tissues in rats with visceral hypersensitivity,so as to study the role of mu opioid receptor in electroacupuncture therapy for IBS.Methods: Thirty-two Sprague-Dawley rats were randomly divided into four groups: normal control group (NC group),model group (M group),model + electroacupuncture group (MEA group) and model + sham electroacupuncture group (MSE group).The visceral hypersensitivity model was established by perfusing acetic acid into rectum.The electromyogram in response to colorectal distension was recorded before and after electroacupuncture (or sham electroacupuncture).The protein expression of mu opioid receptor in proximal colon,distal colon and thalamencephalon tissues was determined by Western blotting.Results: After electroacupuncture,the frequency of electrical activity of abdominal external oblique muscle responding to colorectal distension (20,40,60 and 80 mm Hg) in MEA group was significantly decreased (P0.001),but no significant difference was found before and after sham electroacupuncture in MSE group (P0.05).Compared with M group,the protein expression of mu opioid receptor in MEA group increased significantly in proximal colon,distal colon and thalamencephalon tissues (P0.05),but no significant change was seen in MSE group (P 0.05).Conclusions: Electroacupuncture at ST-36 attenuates visceral hypersensitivity in rats,and its mechanism may be via up-regulating the protein expression of central and peripheral mu opioid receptor.