[Effect of electroacupuncture of "Tianshu"(ST25) at different frequencies on electromyography and immunoactivity of SP and VIP of colon in rats with slow transit constipation].

Objective: To observe the effect of electroacupuncture (EA) of bilateral "Tianshu"(ST25) at different frequencies on the first black stool discharge time, colonic electromyography (EMG) and immunoactivity of vasoactive intestinal peptide (VIP) and substance P (SP) in the colon tissue in rats with slow transit constipation (STC), so as to choose a better stimulating frequency in the treatment of STC.
Methods: A total of 50 male Wistar rats were randomized into control, model, 2 Hz-EA, 100 Hz- EA, and 2 Hz/100 Hz-EA groups, with 10 rats in each group. The STC model was established by intraperitoneal injection of compound diphenoxylate suspension fluid (10 mg/kg). EA was applied to bilateral ST25 for 30 min, once a day for 14 consecutive days. The discharge time for the first black stool was recorded after gavage of mixed suspension fluid of active carbon (2 mL) for assessing the gastrointestinal motility. The colonic EMG was recorded by using a pair of silver electrodes and bioelectric amplifier. The expression of SP and VIP in the colonic tissue was detected by immunohistochemistry.
Results: Following mode-ling, the colonic EMG amplitude, the discharge time for the first black stool and VIP immunoactivity were significantly increased ( P <0.01), and the EMG frequency and SP immunoactivity were significantly decreased （ P <0.01） in the model group compared with the control group. Compared with the model group, the increase of the discharge time for the first black stool, EMG amplitude and VIP immunoactivity, the decrease of EMG frequency and SP immunoactivity were reversed in the 3 EA groups ( P <0.01, P <0.05). The therapeutic effect of 100 Hz-EA was notably weaker than that of both 2 Hz-EA and 2 Hz/100 Hz-EA in up-regulating EMG frequency and SP immunoactivity and in down-regulating the discharge time for the first black stool, EMG amplitude and VIP immunoactivity ( P <0.05, P <0.01). There was no significant difference between the 2 Hz/100 Hz-EA and 2 Hz-EA groups ( P >0.05).
Conclusion: EA can accelerate colonic EMG activities, which may be associated with its functions in down-regulating VIP immunoactivity and up-regulating SP immunoactivity in the colonic tissues. The therapeutic effects of 2 Hz/100 Hz-EA and 2 Hz-EA are better than that of 100 Hz-EA.