: The relationship between analgesic effect of CA and the plasma concentration of Dl-tetrahydropalmatine (dl-THP, active component of CA) was assayed in mice writhing test. The CA (34, 68 and 134 mg/kg) reduced the nociception by acetic acid intraperitoneal injection in a dose-dependent manner, and there was a significant linear relationship between the analgesic effect of CA and the plasma concentration of dl-THP. Then the plasma concentration of dl-THP at different time intervals in rats after oral administration of CA, CA–Cou, CA–VO and CA–Cou–VO were examined by using HPLC.
: The results indicated that Cou and (or) VO raised the plasma concentration of dl-THP prominently. In conclusion, the reason that Radix Angelica dahurica extracts reinforced the analgesic effects of Corydalis alkaloid was related to the improvement of the plasma concentration of dl-THP.