Bioassay-guided evaluation of antinociceptive properties and chemical variability of the essential oil of Hyptis fruticosa.

The composition of three samples of essential oil (EO) extracted from the leaves and flowers of Hyptis fruticosa (Lamiaceae) were investigated by GC/MS and GC-FID. The variability of the constituents and biological activity were evaluated in the oil samples. Acetic acid-induced abdominal constrictions and formalin-induced pain tests in mice were used for screening the antinociceptive activity. The possible antagonism of the essential oils or morphine (MOR) antinociceptive effects by pretreatment with naloxone, showed no influence on the antinociceptive action of the oils in the acetic acid-induced writhing test. All examined oil samples presented antinociceptive activity. The oil sample obtained from the leaves collected during the vegetative growth stage, near São Cristóvão at Sítio Tujubeba exhibited the highest effect. The same oil sample had a main percentage of 1,8-cineole (18.70%). Nevertheless, the oil obtained from flowers collected at the same location, showed a significant difference (p < 0.05) in the response intensity in the first phase of paw licking (100 mg/kg) possibly due to the higher contents of α-pinene (20.51%) and β-pinene (13.64%). The results provide evidence for the use of H. fruticosa by traditional medicine practitioners in the management of pain.