Antinociceptive effect of intrathecal sec-O-glucosylhamaudol on the formalin-induced pain in rats

Background: The root of Peucedanum japonicum Thunb., a perennial herb found in Japan, the Philippines, China, and Korea, is used as an analgesic. In a previous study, sec-O-glucosylhamaudol (SOG) showed an analgesic effect. This study was performed to examine the antinociceptive effect of intrathecal SOG in the formalin test. Methods: Male Sprague-Dawley rats were implanted with an intrathecal catheter. Rats were randomly treated with a vehicle and SOG (10 mu g, 30 mu g, 60 mu g, and 100 mu g) before formalin injection. Five percent formalin was injected into the hind-paw, and a biphasic reaction followed, consisting of flinching and licking behaviors (phase 1, 0-10 min; phase 2, 10-60 min). Naloxone was injected 10 min before administration of SOG 100 mu g to evaluate the involvement of SOG with an opioid receptor. Dose-responsiveness and ED50 values were calculated. Results: Intrathecal SOG showed a significant reduction of the flinching responses at both phases in a dose-dependent manner. Significant effects were showed from the dose of 30 mu g and maximum effects were achieved at a dose of 100 mu g in both phases. The ED50 value (95% confidence intervals) of intrathecal SOG was 30.3 (25.8-35.5) mu g during phase 1, and 48.0 (41.4-55.7) during phase 2. The antinociceptive effects of SOG (100 mu g) were significantly reverted at both phases of the formalin test by naloxone. Conclusions: These results demonstrate that intrathecal SOG has a very strong antinociceptive effect in the formalin test and it seems the effect is related to an opioid receptor.