RT Journal Article
SR Electronic
T1 Effects of clonidine, dexmedetomidine and xylazine on thermal antinociception in rhesus monkeys.
JF Journal of Pharmacology and Experimental Therapeutics
JO J Pharmacol Exp Ther
FD American Society for Pharmacology and Experimental Therapeutics
SP 762
OP 769
VO 264
IS 2
A1 E R Butelman
A1 J H Woods
YR 1993
UL http://jpet.aspetjournals.org/content/264/2/762.abstract
AB The antinociceptive effects of the s.c. administration of the alpha-2 agonists clonidine (0.0032-1.0 mg/kg), dexmedetomidine (0.001-0.032 mg/kg) and xylazine (0.1-3.2 mg/kg) were examined in the warm-water tail withdrawal assay in rhesus monkeys. The three agonists were dose-dependently effective in this assay; their potency order being dexmedetomidine > clonidine > xylazine. The alpha-2 antagonist idazoxan (0.1-3.2 mg/kg) caused dose-dependent and roughly parallel rightward shifts in the dose-effect curves for the three agonists. Apparent pA2 analysis with idazoxan yielded homogeneous values for the three agonists, supporting the notion that similar receptors mediate their antinociceptive effects. The opioid antagonist quadazocine (1.0 mg/kg) did not antagonize the antinociceptive effects of clonidine and xylazine, indicating that opioid receptors do not participate in the effects of the compounds in this assay. At dose ranges found to be effective in the antinociceptive assay, clonidine, dexmedetomidine and xylazine also dose-dependently caused sedation, muscle relaxation, bradycardia and moderate respiratory depression. The sedative, muscle relaxant and respiratory depressant effects of xylazine could be antagonized by idazoxan, suggesting that these effects may be mediated through alpha-2 receptors. These data indicate that the three imidazoline alpha-2 agonists, clonidine, dexmedetomidine and xylazine are effective s.c. in the warm-water tail withdrawal assay in rhesus monkeys, but only at doses that produce other behavioral and physiological effects.