Effects of α2-adrenergic drugs on small intestinal motility in the horse: an in vitro study.

The effects of selective α(2)-agonists (xylazine, detomidine and medetomidine) and antagonists (yohimbine and atipamezole) on in vitro small intestine motility in the horse were evaluated. Samples of equine jejunum were placed in isolated organ baths and drug-induced modifications of motility were measured by means of an isotonic transducer. All tested α(2)-agonists dose-dependently reduced both spontaneous and electrically-evoked phasic contractions. Conversely, α(2)-antagonists were ineffective when tested alone, and showed a heterogeneous and dose-independent ability to inhibit agonist activity. In particular, the antagonism exerted by higher concentrations of both yohimbine and atipamezole against α(2)-agonists was weaker than when lower concentrations were used. The data are indicative of the presence of both pre- and post-synaptic α(2)-adrenoceptors with inhibitory activity on equine jejunum motility, and support a possible therapeutic utility of these drugs in horse intestinal disorders associated with hypermotility.