Antinociceptive effects of an ethyl acetate soluble fraction of Spirodela polyrrhiza

Spirodela polyrrhiza L. Schleid. (Lemnaceae), also known as 'duckweed', is a traditional medicine in Korea. The whole plant is used to treat many diseases, including the common cold, edema, acute nephritis, and urticaria. The present study investigated antinociceptive properties of the EtOAc soluble fraction of S. polyrrhiza (ESP). The antinociceptive activities of ESP were studied using experimental models of pain, including thermal nociception methods, such as the tail immersion test and the hotplate test. Moreover, we studied chemical nociception induced by intraperitoneal acetic acid and subplantar formalin in mice. ESP exhibited dose-dependent antinociceptive activity in both thermal and chemical pain models. In a drug combination test using the opioid receptor antagonist naloxone, diminished analgesic activities of ESP were observed, indicating that the antinociceptive activity of ESP is mediated by opioid receptors.