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.