OBJECTIVETo observe the analgesic effect of Zhitong Capsule (ZTC) and study its mechanism in adjuvant arthritis (AA) rats.

METHODSForty-eight male Sprague-Dawley rats were randomly divided into six groups with 8 rats in each group. On the first day, except to those in the normal group that were treated with normal saline, the same amount of Freund's complete adjuvant (FCA) was given through intradermal injection into the right hind paw to all the rats in the other groups. From the 17th day of the modeling on, the rats in groups of ZTC were administered daily through gastrogavage with a dose of 1000, 500, 250 mg/kg respectively, while equal volume of normal saline was given to those in the normal group and model group, and an equal volume of aspirin (ASA) solution was given to rats in the ASA group through gastrogavage for 10 days, once per day, and on the 27th day, the analgesic effect of ZTC was measured with heat withdraw method. The activities and contents of superoxide dismutase (SOD) and lipid peroxides (LPO) in serum were observed by spectrophotometry, and the level of beta-endorphin (beta-EP) in hypothalamus were determined by the assay of immunohistochemistry.

RESULTSZTC showed significant effects on enhancing the pain threshold and at the same time it increased the activities of SOD and reduced the contents of LPO in serum. ZTC could also increase the level of beta-EP in hypothalamus.

CONCLUSIONZTC has analgesic effect and its mechanism is probably related with its effect in inhibiting the level of oxygen free radicals in serum and increasing the level of beta-EP of hypothalamus in rats.