Antinociceptive actions of intravenous a2-adrenoceptor agonists in sheep

Abstract

The aminociceptive activity of the intravenously administered .alpha.2-adrenoceptor agonists, clonidine and xylazine, was measured in sheep using thermal and mechanical pressure threshold detection systems. Both drugs demonstrated clear antinociceptive activity for both forms of threshold stimuli and clonidine at 6 .mu.g/kg i.v. was more potent and longer lasting than xylazine at 50 .mu.g/kg i.v. The antinociceptive effects were reversed by idazoxan (0.1 mg/kg i.v.), but were not affected by naloxone at 0.2 mg/kg i.v. indicating that these effects were mediated by .alpha.2-adrenoceptors.