Pain threshold pressure (PTP) measured in response to colorectal distension showed a significant difference between the one‐off electroacupuncture (EA) and repetitive EA groups, and also between the chronic visceral hypersensitivity (CVH) and control groups. Data are mean (SEM); *p<0.05 versus one‐off EA, †p<0.05 versus normal. CVH was induced by neonatal colon irritation. PTP was measured by the abdominal withdrawal reflex to assess the response of chronic visceral hypersensitivity to a mechanical visceral stimulus. EA treatment was applied on ST36 and SP6 acupoints bilaterally with 2 Hz, 0.3 mA, lasting 30 minutes. One‐off EA was applied for 30 minutes only once, while repetitive EA was done for 30 minutes per day for seven days. PTP in response to CRD was 37.4 (3.5) mm Hg in the CVH group (n = 6) and 53.2 (6.0) mm Hg in the normal group. Thus there was a significant difference in rectal sensitivity to CRD between normal controls and the CVH group, suggesting that the CVH model was reliable. Repetitive EA treatment significantly raised PTP compared with one‐off EA treatment. PTP in response to CRD was 62.7 (4.3) mm Hg in the one‐off EA treatment group (n = 6) and 75.1 (2.8) mm Hg in the repetitive EA treatment group (n = 6), suggesting that repetitive treatment is more effective than one‐off EA treatment for CVH.

 5‐Hydroxytryptamine (5‐HT) concentrations were detected in three groups involving normal rats, chronic visceral hypersensitivity (CVH) rats, and electroacupuncture (EA) treatment of CVH rats. CVH elevated 5‐HT concentrations in the colon, accompanied by diminished PTP (fig 1). EA decreased 5‐HT concentrations in CVH rats accompanied by elevated PTP (fig 1). Data are mean (SEM). *p<0.05 versus normal, †p<0.05 versus CVH. 5‐HT content of the colon was assayed fluorimetrically using o‐phthalaldehyde, which forms a fluorescent complex with 5‐HT. Chronic visceral hypersensitivity raised 5‐HT concentrations in the colon, which were significantly reduced by EA, accompanied by elevated PTP. There were significant differences in 5‐HT concentrations in the colon in three groups: 12.53 (6.45) ng in the normal group (n = 6), 38.64 (8.01) ng in the CVH group (n = 6), and 25.12 (8.82) ng after EA treatment in the CVH group (n = 6). These results suggest that EA can reduce 5‐HT content in the colon, while elevating PTP, indicating that peripheral 5‐HT, especially in the gastrointestinal tract, takes part in the analgesic effect of EA.