Objective: To observe the regularity of electroacupuncture(EA) analgesia and to analyze its relation to hypothalamus-pituitary-adrenal cortex axis function in chronic constrictive injury(CCI) and ovariectomy(OVX) rats.Methods: A total of 110 Wistar rats anesthetized with mixture solution of 1.5% chloralose(50 mg/kg) and 25% urethrane(420 mg/kg

i.p.) were randomized into control(n=10)

CCI(n=10)

CCI+EA(n=30)

OVX+CCI(n=30)

OVX+CCI+EA(n=30) groups

and the later 3 groups were further divided into 2 times(2 t)

2 weeks(2 w)and 3 w time courses

with 10 cases in each.Forty-five days after OVX

Morris water maze test was conducted to evaluate the OVX rats' memory-learning ability.Chronic pain model was established by ligating the right sciatic nerve with a piece of suture.EA(2/15 Hz

1 mA) was applied to bilateral "Zusanli"(ST 36)-"Yanglingquan"(GB 34) for 30 min

once daily for 2 t

2 w

3 w respectively.The paw withdrawal latency(PWL) was detected to be used as the pain threshold.Under deep anesthesia

the rat was decapitated for collecting blood samples.Plasma adrenocorticotropic hormone(ACTH)

β-endorphine(EP)

cortisone(COR) contents were detected using radioimmunoassay.Results: In comparison with control group

PWL difference values(PWLDV) of CCI+EA

OVX+CCI and OVX+CCI+EA groups increased significantly(P<0.05)

suggesting a marked decrease of pain threshold.Compared with CCI group

PWLDV of CCI+EA group at 3 w decreased significantly(P<0.05)

being close to normal control group(P>0.05).Compared with OVX+CCI group

PWLDV of OVX+CCI+EA at 2 w and 3 w lowered significantly(P<0.05)

suggesting an evident pain relief.In comparison with CCI+EA group

PWLDV of OVX+CCI+EA group at most time courses were considerably higher(P<0.05)

showing a better cumulative analgesic effect in CCI rats without OVX.In CCI group

plasma β-EP increased slightly

ACTH had no clear changes

and COR lowered lightly at 2 t.No significant differences were found between control and CCI+EA groups in β-EP and ACTH levels at 2 w and 3 w(P>0.05)

only COR levels of CCI+EA group at 2 w and 3 w increased significantly(P<0.05).Compared with control group

β-EP levels of OVX+CCI group at 2 w and 3 w increased significantly(P<0.05);plasma ACTH had no marked changes(P>0.05);COR contents of OVX+CCI group decreased evidently at 2 t and increased markedly at 2 w(P<0.05).Compared with OVX+CCI group

in OVX+CCI+EA group

β-EP levels of 2 t and 2 w decreased significantly(P<0.05);ACTH levels increased evidently at 2 t and 3 w

and decreased markedly at 2 w(P<0.05);and COR level at 2 w decreased significantly(P<0.05).It indicated that when cumulative EA analgesia appeared

in CCI animals

only plasma COR level increased pronouncedly

while in OVX+CCI rats

both plasma β-EP and COR contents decreased evidently.Conclusion: Both plasma β-EP and COR are involved in the accumulative analgesic effect of EA in the rat

and decline of learning memory ability may weaken the analgesic effect of EA to a certain degree

but no clear correlation tendency is found between changes of plasma β-EP and COR and the improvement of pain behavior.