Objective To observe the effect of electroacupuncture(EA)on mechanical hyperalgesia threshold(MHTs)and thermal hyperalgesia threshold(THTs)and content of proteinase-activated receptors 2(PAR 2)in dorsal root ganglia(DRG)in rats with inflammatory pain

so as to explore its peripheral mechanism underlying improvement of inflammatory pain.Methods The present study contains two parts.1)In the first part

27 male SD rats were randomized into sham hyperalgesic priming(shamHP)group and real hyperalgesic priming(HP)group(n=5 in the sham-HP group and n=6 in the HP group for the test of MHTs

n=8 in the two groups for the test of THTs).The sham-HP model was established by subcutaneous injection of normal saline into the left plantar part of the hind-paw

and the HP model established by subcutaneous injection of 1%carragenan(the first injection)into the same left hind paw

followed by injection of PGE2(100 ng/25μL

the second injection)into the dorsum pedis of the same hind paw 7 days after the first injection.The ipsilateral paw withdrawal latencies(MHTs and THTs)were detected before and 5 h

3 dand 6 dafter the first injection

0.5

4 and 24 hafter the second injection.2)In the second part

64 male SD rats were randomly divided into sham-HP

HP

sham-EA and EA groups(n=16 in each group).The sham-HP and HP models were made in the same way as the first part.Both"Zusanli"(ST 36)and"Kunlun"(BL 60)were punctured with filiform needles in the sham-EA group and also stimulated with EA:2 Hz/100 Hz

0.5-1.5 mA(0.5 mA increase per 10 min)for 30 min in the EA group

1 time/d for7 d.Both ipsilateral MHTs and THTs were observed at the same time-points of the first part and the PAR 2 protein content in the L 4-L 6 DRGs was assayed by ELISA 24 hafter the second injection.Results 1)In the first part of the study

compared with the sham-HP group

the MHTs at 5 hand 3 d

and THT at 5 hafter the first injection

and MHTs

and THTs at 4 and 24 hafter the second injection were significantly decreased in the HP group(P<0.01

P<0.05).2)In the second part of the study

compared with the HP group

the MHTs at 4 and 24 hafter the second injection and the THTs at 3 dafter the first injection

4 and 24 hafter the second injection were significantly up-regulated in the EA group(P<0.01

P<0.05).The content of PAR 2 in the DRGs(L 4-L 6)was significantly higher in the HP group than in the sham-HP group(P<0.05)

but considerably lower in the EA group than in the HP group(P<0.05).Conclusion EA can suppress hyperalgesia priming in inflammatory pain rats which may be related to its effect in down-regulating PAR 2 level in the lumbar DRGs.