Our previous work has shown that opiate-like substance(OLS)is involved in the centralmechanism of acupuncture analgesia(AA)in the arthritic rats.In this paper

the role of OLS inperipheral mechanism of AA is further studied.Twenty four hours after a subcutaneous injectionof Freund's adjuvant into the right ankles

acute arthritis with typical symptoms developed in allthe rats.Following needling at Huantiao points for 10 minutes

the pain threshold(PT)wasraised by 42. 3%(P<0.05)in the inflammed ankles and by 5.6% in the non-inflammed ones.When systemically administered a dose of 250 and 100μg

naloxone(Nx)could completely andpartially(49.6%)block AA respectively.While locally injected a dose of 100μg even 20μg

Nxcould completely antagonize AA.After systemic administration of morphine(10

5.0

2.5

1.25mg/kg)

PT rise was dose-related

and PT was raised by 86.5±22.7% in the affected anklesand by 32.9±14.9% in the normal ankles at 5 mg/kg in dose.It is evident that the opiate recep-tors in the imflammed area should by sensitized.These results demonstrate that activation of en-dogenous opiate system may also be involved in the peripheral AA.Acupuncture may enhance therelease of peripheral OLS which can act at the sensitized opiate receptors

leading to more potentanalgesic effect in the inflammed area.