Antinoceptive effect of triterpenoid α, β-amyrin in rats on orofacial pain induced by formalin and capsaicin

• Published in: Phytomedicine (Stuttgart) Vol. 15; no. 8; pp. 630 - 634
• Main Authors: Holanda Pinto, S.A., Pinto, L.M.S., Guedes, M.A., Cunha, G.M.A., Chaves, M.H., Santos, F.A., Rao, V.S.
• Format: Journal Article
• Language: English
• Published: Germany Elsevier GmbH 01.08.2008; Urban & Fischer Verlag
• Subjects: Analgesics - administration & dosage; Analgesics - chemistry; Analgesics - therapeutic use; Animals; Antinociception; Burseraceae - chemistry; Capsaicin; Capsaicin - toxicity; Chemical properties; Dose-Response Relationship, Drug; Drug Administration Schedule; Drug therapy; Facial pain; Facial Pain - chemically induced; Facial Pain - prevention & control; Formaldehyde - toxicity; Formalin; Health aspects; Male; Molecular Structure; Oleanolic Acid - administration & dosage; Oleanolic Acid - analogs & derivatives; Oleanolic Acid - chemistry; Oleanolic Acid - therapeutic use; Orofacial pain; Phytotherapy; Protium heptaphyllum; Rats; Rats, Wistar; Risk factors; Terpenes; α, β-Amyrin; Brazil; Formalin; Antinociception; α, β-Amyrin; Orofacial pain; Capsaicin; Protium heptaphyllum
• ISSN: 0944-7113; 1618-095X
• DOI: 10.1016/j.phymed.2007.11.016

The effects of α, β-amyrin, a pentacyclic triterpene isolated from Protium heptaphylum was investigated on rat model of orofacial pain induced by formalin or capsaicin. Rats were pretreated with α, β-amyrin (10, 30, and 100 mg/kg, i.p.), morphine (5 mg/kg, s.c.) or vehicle (3% Tween 80), before formalin (20 μl, 1.5%) or capsaicin (20 μl, 1.5 μg) injection into the right vibrissa. In vehicle-treated controls, formalin induced a biphasic nociceptive face-rubbing behavioral response with an early first phase (0–5 min) and a late second phase (10–20 min) appearance, whereas capsaicin produced an immediate face-rubbing (grooming) behavior that was maximal at 10–20 min. Treatment with α, β-amyrin or morphine significantly inhibited the face-rubbing response in both test models. While morphine produced significant antinociception in both phases of formalin test, α, β-amyrin inhibited only the second phase response, more prominently at 30 mg/kg, in a naloxone-sensitive manner. In contrast, α, β-amyrin produced much greater antinociceptive effect at 100 mg/kg in the capsaicin test, which was also naloxone-sensitive. These results provide first time evidence to show that α,β-amyrin attenuates orofacial pain atleast, in part, through a peripheral opioid mechanism but warrants further detailed study for its utility in painful orofacial pathologies.