Characterisation of the anti-inflammatory and antinociceptive activities of the Hyptis pectinata (L.) Poit essential oil

Abstract

Hyptis pectinata Poit (Lamiaceae) is grown in the northeastern regions of Brazil and is popularly known as "sambacaitá" or "canudinho". It is extensively used in folk medicine to treat inflammatory conditions, bacterial infections, pain, and cancer. Hyptis pectinata essential oil (EO, 10, 30, and 100mg/kg, p.o.) and the reference drugs morphine (5mg/kg, p.o.) and acetylsalicylic acid (ASA, 200mg/kg, p.o.) were evaluated using models for analgesia (acetic acid-induced contortions and hot plate) or inflammation (formalin-induced licking response and the subcutaneous air-pouch model). To elucidate the EO's mechanism of action, animals were pre-treated with the opioid receptor antagonist naloxone (1mg/kg, i.p.), the cholinergic antagonist atropine (1mg/kg, i.p.), or l-nitro arginine methyl ester (l-NAME, 3mg/kg, i.p.) 30 min prior to the oral administration of the EO. The EO significantly inhibited the number of writhings and the time the animals spent licking their formalin-injected paws (second phase). The EO, at doses of 30 and 100mg/kg, increased baseline measurements and area under the curve measurements in the hot plate model, respectively. The administration of naloxone reversed the antinociceptive effect of the EO in the hot plate model. l-NAME significantly reversed the effects of the EO in the contortions and hot plate models. Atropine completely reversed the antinociceptive activity of the EO in all models. Additionally, the EO inhibited the inflammatory process induced by subcutaneous carrageenan injection by reducing cell migration, exudate volume, protein concentration, and inflammatory mediators (nitric oxide, prostaglandin E2, IL-6, and TNF-α) produced in the pouch. Our results indicate that the Hyptis pectinata essential oil exhibits antinociceptive effects, likely mediated by opioid and cholinergic receptors, and anti-inflammatory activity through the inhibition of nitric oxide and PGE2 production.