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 µg, 30 µg, 60 µg, and 100 µg) 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 µg 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 µg and maximum effects were achieved at a dose of 100 µg in both phases. The ED50 value (95% confidence intervals) of intrathecal SOG was 30.3 (25.8–35.5) µg during phase 1, and 48.0 (41.4–55.7) during phase 2. The antinociceptive effects of SOG (100 µg) 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.