Antinociceptive activity of Annona diversifolia Saff. leaf extracts and palmitone as a bioactive compound.

Annonas are consumed as fresh fruits, but are also widely used in folk medicine for treating pain and other ailments. Antinociceptive properties of the Annona diversifolia ethanol crude extract were tested using the pain-induced functional impairment model in rat (PIFIR) and the writhing test in mice. The ethanol extract caused a 25% recovery of limb function in rats; this response was significant and dose-dependent. Furthermore, this extract produced a similar antinociceptive response (ED(50)=15.35 mg/kg) to that of the reference drug tramadol (ED(50)=12.42 mg/kg) when evaluated in the writhing test in mice. Bio-guided fractionation yielded hexane and acetone active fractions from which the presence of palmitone and flavonoids was respectively detected. Palmitone produced an antinociceptive response with an ED(50)=19.57 mg/kg in the writhing test. Antinociceptive responses from ethanol extract and tramadol were inhibited in the presence of either naloxone (1mg/kg, s.c.)--an antagonist of endogenous opioids--or WAY100635 (0.8 mg/kg, s.c.)--a 5-HT(1A) serotonin receptor antagonist. These results provide evidence that A. diversifolia possesses antinociceptive activity, giving support to their traditional use for treatment of spasmodic and arthritic pain. In addition, our results suggest the participation of endogenous opioids and 5-HT(1A) receptors in this antinociceptive response.