Antinociceptive activities of the liposoluble fraction from Vitex negundo seeds

The antinociceptive activities of the petroleum ether fraction (PEF) from the aqueous ethanol extract of Vitex negundo Linn. (Verbenaceae) seeds have been evaluated in several nociceptive mouse models. Given orally, the PEF (at doses of 12, 24, and 48 mg/kg body weight) produced significant dose-related inhibitions on chemical nociception induced by intraperitoneal acetic acid and sub-plantar formalin injections and on thermal nociception in the hot-plate test. Naloxone (1 mg/kg bw subcutaneously), a non-selected opioid receptor antagonist, notably reversed the analgesic effect caused by the PEF (48 mg/kg bw) when assessed against the first phase of the formalin test, but this effect was less significant for the PEF in the second phase. Our observations suggest that the PEF probably interacted with the opioid system and may be more effective on inflammatory pain. In addition, potent anti-inflammatory activity of the PEF was observed in the xylene-induced ear edema test, which further indicates that the analgesic effects of the PEF may be partially mediated by its anti-inflammatory activity. Further chemical analysis suggests that the analgesic activities of the PEF could be mostly due to the abundance of fatty acids with synergetic effects in the present work.