Antinociceptive effect of the essential oil of Lippia sidoides on mice

Lippia sidoides Cham. (Verbenaceae), an aromatic medicinal shrub, is used in Brazilian folk medicine to combat bacterial infections, inflammation and pain [1]. The aim of this study was to investigate the possible analgesic effect of Lippia sidoides essential oil on two pain models in mice, namely acetic acid-induced writhing [2] and hot-plate [3] tests. Leaves of L. sidoides were collected in São Cristóvão county (10€56'S, 37€05'W), Brazil. Essential oil was obtained by steam distillation in a Clevenger-type apparatus (4.1% yield) and analyzed by gas chromatography/mass spectroscopy. p-Cymene (26.8%), thymol (21.9%) e myrcene (12.8%) are identified as the major constituents. A dose-related antinociceptive effect was obtained in the acetic acid-induced writhing test at doses of 100, 200, and 400mg/kg (s.c.; p>0.5; p<0.05; p<0.01, respectively). In the hot-plate test, the essential oil (25–200mg/kg; s.c.) significantly increased the latency at doses of 100 (p<0.05) and 200mg/kg (p<0.01). The essential oil-induced antinociception in hot-plate test (200mg/kg; s.c.) was antagonized by naloxone (3mg/kg; i.p.). In conclusion, the essential oil of Lippia sidoides showed antinociceptive effect in chemical and thermal models of nociception in mice. The activation of opioidergic system appears to play a crucial role in the observed antinociceptive effect.

Acknowledgments: CNPq.

References: 1. Girão, V.C.C. et al. (2003), Preventive Veterinary Medicine 59: 95. 2. Koster, R. et al. (1959), Fed. Proc. 18: 412. 3. Ankier, S.I. (1974), Eur. J. Pharmacol. 27: 1.