The effects of α2-adrenoceptor agents on anti-hyperalgesic effects of carbamazepine and oxcarbazepine in a rat model of inflammatory pain

In this study, the effects of yohimbine (alpha2-adrenoceptor antagonist) and clonidine (alpha2-adrenoceptor agonist) on anti-hyperalgesia induced by carbamazepine and oxcarbazepine in a rat model of inflammatory pain were investigated. Carbamazepine (10-40 mg/kg; i.p.) and oxcarbazepine (40-160 mg/kg; i.p.) caused a significant dose-dependent reduction of the paw inflammatory hyperalgesia induced by concanavalin A (Con A, intraplantarly) in a paw pressure test in rats. Yohimbine (1-3 mg/kg; i.p.) significantly depressed the anti-hyperalgesic effects of carbamazepine and oxcarbazepine, in a dose- and time-dependent manner. Both drug mixtures (carbamazepine-clonidine and oxcarbazepine-clonidine) administered in fixed-dose fractions of the ED50 (1/2, 1/4 and 1/8) caused significant and dose-dependent reduction of the hyperalgesia induced by Con A. Isobolographic analysis revealed a significant synergistic (supra-additive) anti-hyperalgesic effect of both combinations tested. These results indicate that anti-hyperalgesic effects of carbamazepine and oxcarbazepine are, at least partially, mediated by activation of adrenergic alpha2-receptors. In addition, synergistic interaction for anti-hyperalgesia between carbamazepine and clonidine, as well as oxcarbazepine and clonidine in a model of inflammatory hyperalgesia, was demonstrated.