Peripheral and central effects of dexrnedetomidine, a specific alpha-2 adrenergic agonist, oil phasic and tonic pain

Recently, vast studies have been focused on the antinociceptive and anesthetic effects of α2 adrenergic receptors, using specific drugs such as medetomidine and dexmedetomidine. In the present study, we tried to assess the peripheral and central effects of dexmedetomidine in phasic and tonic pain, on rats, using tail flick and formalin tests. Dexmedetomidine, administered intraperitoneally (25, 50 and 100 µg/kg, i.p.) or intracerebroventrically (7.5, 10 and 20 µg, i.c.v.) induced total anesthesia. This effect could be seen by 10 and 20 µg, i.c.v. doses of the drug in spinal animals, too, which was reversed by 5 µg, i.c.v. of yohimbine. Dexmedetomidine (6.5 µg, i.c.v. or 20 µg, i.p.) showed antinociceptive effects in formalin test which was reversed by yohimbine (5 µg, i.c.v.). Dexmedetomidine (5, 6.5, 7.5, 10 and 20 µg, i.c.v. or 20, 25, 50 and 100 µg/kg, i.p.) had significant antinociceptive effects in tail flick test, which could be reversed by 5 µg, i.c.v. administration of yohimbine. The results of tail flick test in the spinal animals, shows that dexmedetomidine (6 µg, i.c.v.) in these animals induces antinociception, which was reversed by yohimbine pretreatment (1 mg/kg, i.p.). These results indicate that, dexmedetomidine probably exerts, its antinociceptive effect, through spinal α2 adrenergic receptors.