Objective To investigate the effect of electroacupuncture(EA) of "Sanyinjiao"(SP 6) on the uterus in dysmenorrhea rats so as to study its underlying analgesic mechanism.Methods A total of 48 SD rats during diestrus were randomized into normal saline(control) group

model group and acupuncture group according to a random number table

with 16 rats in each group.Dysmenorrhea model was established by subcutaneous injection of Estradiol benzoate(0.5 mg/d on the 1st and 10th day

and 0.2 mg/d from day 2 to day 9

once daily for 10 days) and oxytocin(2 U/rat

once on day 10).Malondialdehyde(MDA) and β-endorphin(β-EP) contents in the uterus were detected by radioimmunoassay

and the heat shock protein 70(HSP 70) immunoactivity of the uterus was detected by immunohistochemistry.Results In comparison with the control group

MDA content in the uterus was increased significantly in the model group(P<0.01)

while the β-EP level and the immunoactivity of HSP 70 immuno-reaction(IR) positive products in the uterus decrease significantly(P<0.01)and moderately

respectively in the model group.In comparison with the model group

uterine MDA content in the EA group was decreased significantly(P<0.01)

while uterine β-EP level increased considerably(P<0.01)and HSP 70 expression was upregulated to a certain degree.Conclusion EA of "Sanyinjiao"(SP 6) can reduce MDA content and upregulate β-EP level of the uterus in rats with dysmenorrhea

which may contribute to its analgesic effect in relieving dysmenorrhea by clearing away oxygen free radicals and raising analgesic substance in the uterus.