title: Antinoceptive effect of triterpenoid alpha,beta-amyrin in rats on orofacial pain induced by formalin and capsaicin.
abstract: The effects of alpha,beta-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 alpha,beta-amyrin (10, 30, and 100mg/kg, i.p.), morphine (5mg/kg, s.c.) or vehicle (3% Tween 80), before formalin (20 microl, 1.5%) or capsaicin (20 microl, 1.5 microg) 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 alpha,beta-amyrin or morphine significantly inhibited the face-rubbing response in both test models. While morphine produced significant antinociception in both phases of formalin test, alpha,beta-amyrin inhibited only the second phase response, more prominently at 30 mg/kg, in a naloxone-sensitive manner. In contrast, alpha,beta-amyrin produced much greater antinociceptive effect at 100mg/kg in the capsaicin test, which was also naloxone-sensitive. These results provide first time evidence to show that alpha,beta-amyrin attenuates orofacial pain at least, in part, through a peripheral opioid mechanism but warrants further detailed study for its utility in painful orofacial pathologies.
authors.affiliation: Department of Physiology and Pharmacology, Post-Graduation Programme in Medical Sciences, Faculty of Medicine, Federal University of Ceara, POB 3157, Rua Cel Nunes de Melo-1127, Porangabussu, 60430-270 Fortaleza, Ceara, Brazil.
authors.forename: S A
authors.initials: SA
authors.lastname: Holanda Pinto
authors.forename: L M S
authors.initials: LM
authors.lastname: Pinto
authors.forename: M A
authors.initials: MA
authors.lastname: Guedes
authors.forename: G M A
authors.initials: GM
authors.lastname: Cunha
authors.forename: M H
authors.initials: MH
authors.lastname: Chaves
authors.forename: F A
authors.initials: FA
authors.lastname: Santos
authors.forename: V S
authors.initials: VS
authors.lastname: Rao
mesh_terms: D000700:Analgesics / Q000008:administration & dosage / Q000737:chemistry / Q000627:therapeutic use; D000818:Animals; D029403:Burseraceae / Q000737:chemistry; D002211:Capsaicin / Q000633:toxicity*; D004305:Dose-Response Relationship, Drug; D004334:Drug Administration Schedule; D005157:Facial Pain / Q000139:chemically induced* / Q000517:prevention & control*; D005557:Formaldehyde / Q000633:toxicity*; D008297:Male; D015394:Molecular Structure; D009828:Oleanolic Acid / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000737:chemistry / Q000627:therapeutic use; D008517:Phytotherapy; D051381:Rats; D017208:Rats, Wistar
chemical_list: D000700:Analgesics; D005557:Formaldehyde; D009828:Oleanolic Acid; C036380:beta-amyrin; D002211:Capsaicin