The effect of xylazine on the isolated sheep trachea

The effect of xylazine on the isolated sheep trachea and its possible interactions with the α₂-adrenergic antagonist, atipamezole, and the anticholinergic agent, atropine, was studied. The mechanical responses of the tracheal preparations were recorded after exposing each one to cumulatively increasing concentrations of xylazine alone or in the presence of atipamezole or atropine.
Xylazine exerted a concentration-dependent contractile effect, with a threshold concentration of 10^--⁷M while the maximum activity was produced at a concentration of 10^--⁵M (EC₅₀= 2.3 × 10^--⁷). This xylazine-induced contractile effect was inhibited by atipamezole, but not significantly modified by atropine. Thus, it is concluded that α₂-adrenoceptors exist in the sheep trachea and it is suggested that α₂-adrenoceptor agonists may act on airways in sheep directly through stimulation of peripheral α₂-adrenergic receptors and indirectly via central α₂-adrenergic receptor activation of parasympathetic tone.