[The role of OLS in peripheral acupuncture analgesia in arthritic rats]

Our previous work has shown that opiate-like substance (OLS) is involved in the central mechanism of acupuncture analgesia (AA) in the arthritic rats. In this paper, the role of OLS in peripheral mechanism of AA is further studied. Twenty four hours after a subcutaneous injection of Freund's adjuvant into the right ankles, acute arthritis with typical symptoms developed in all the rats. Following needling at Huantiao points for 10 minutes, the pain threshold (PT) was raised by 42.3% (P < 0.05) in the inflamed ankles and by 5.6% in the non-inflamed ones. When systemically administered a dose of 250 and 100 micrograms, naloxone (Nx) could completely and partially (49.6%) block AA respectively. While locally injected a dose of 100 micrograms even 20 micrograms, Nx could completely antagonize AA. After systemic administration of morphine (10, 5.0, 2.5, 1.25 mg/kg), PT rise was dose-related, and PT was raised by 86.5 +/- 22.7% in the affected ankles and by 32.9 +/- 14.9% in the normal ankles at 5 mg/kg in dose. It is evident that the opiate receptors in the inflamed area should by sensitized. These results demonstrate that activation of endogenous opiate system may also be involved in the peripheral AA. Acupuncture may enhance the release of peripheral OLS which can act at the sensitized opiate receptors, leading to more potent analgesic effect in the inflamed area.