Investigation of antinociceptive mechanism caused by mitragynine (major constituent of mitragyna speciosa extract) in mice / Putri Nur Nadiah Megat Mohd Ghazali

Mitragyna speciosa is classified under the family of Rubiaceae (Matsumoto et al., 1996). In folk medicine, it can be used to treat diarrhea and alleviate pain from cutting wounds (Kumarnsit et al., 2006). Farmers, laborers, and peasants tend to use the plant for its anti-fatigue effects and used to enhance physical performances (Kumarnsit et al., 2006). Mitragynine is composed of about 66% of the total alkaloids extracted from the young leaves of the plant (Matsumoto et al., 1996, Matsumoto et al., 2005). Its' young leaves contain mitragynine and are chewed, smoked or drank as tea to produce its'opiod­ like effects (Matsumoto et al., 1996). Mitragynine was found to act as an agonist at the opiod receptor (Kumarnsit et al., 2006, Matsumoto et al., 2005) and can produce antinociceptive effect (Matsumoto et al., 1996) while the antinociceptive effect of mitragynine administered i.c.v was found to be maximal at about 15 minutes after administration and may last to 45 minutes. This study was done to evaluate the analgesic effect of Mitragyna speciosa using the tail-flick test method. From the data collected, the mice treated with MS extract at dose of I 5mg/kg, 25mg/kg and 35mg/kg and 35mg/kg administered paracetamol showed significant difference in response (P value < 0.05) compared to mice treated with saline 0.9% 0.01 mg/kg that act as a control. This occurred at the minutes of 20th, 40th and 70th. The mean reaction times are higher in MS extract at all doses compared to paracetamol starting from the 20th until the 60th minutes. The mean reaction time of saline remains the lowest during the study period. This study also showed that at the 10th and 20th minutes after dose, 25mg/kg MS extract treated mice have the highest mean reaction time followed by the dose of 15mg/kg and 35mg/kg. At the 30th until 50th minutes, the result was 15mg/kg MS extract has the highest mean reaction time followed by MS extract 35mg/kg, 25mg/kg and paracetamol 35mg/kg. This may suggests that MS extract exerts higher potency than paracetamol in the antinociceptive activity. It is likely to have the potential to replace morphine as an analgesic (Matsumoto et al., 1996, Yamamoto et al., 1999).