Xylazine-induced delay of small intestinal transit in mice.
Subcutaneous injection of xylazine (0.1-3.0 mg/kg) produced a dose-dependent delay of small intestinal transit without affecting gastric emptying in the conscious mice. The xylazine-induced delay of small intestinal transit was antagonized by alpha 2-adrenoceptor antagonists, e.g., yohimbine, piperoxan and tolazoline. The antagonism of xylazine activity by yohimbine was dose-dependent, and the maximal antagonistic effect was seen at 1 mg/kg. Other adrenoceptor antagonists with only alpha 1-blocking activity, e.g., thymoxamine, prazosin and phenoxybenzamine at the doses studied did not reduce the depressant effect of xylazine on small intestinal transit. A beta-adrenergic antagonist, propranolol was not effective in reducing xylazine activity. The opioid antagonist, naloxone did not reduce the effective of xylazine, nor did yohimbine antagonize the morphine-induced delay of small intestinal transit. The xylazine-induced delay of small intestinal transit was not altered by atropine, hexamethonium, haloperidol, methysergide, chlorpheniramine or cimetidine. Pretreatment of mice with reserpine and alpha-methyl-p-tyrosine or 6-hydroxydopamine failed to reduce the intestinal effect of xylazine. These results suggest that xylazine-induced delay of small intestinal transit is mediated by postjunctional alpha 2-adrenoceptors and appears not to involve activation of opioid, cholinergic, dopaminergic, histaminergic, or serotonergic receptors.
D000818:Animals; D005746:Gastric Emptying / Q000187:drug effects; D005769:Gastrointestinal Motility / Q000187:drug effects*; D006892:Hydroxydopamines / Q000494:pharmacology; D008297:Male; D008781:Methyltyrosines / Q000494:pharmacology; D051379:Mice; D009270:Naloxone / Q000494:pharmacology; D012110:Reserpine / Q000494:pharmacology; D013563:Sympathectomy, Chemical; D013565:Sympatholytics / Q000494:pharmacology; D013843:Thiazines / Q000494:pharmacology*; D014991:Xylazine / Q000494:pharmacology*; D019805:alpha-Methyltyrosine
D006892:Hydroxydopamines; D008781:Methyltyrosines; D013565:Sympatholytics; D013843:Thiazines; D014991:Xylazine; D009270:Naloxone; D019805:alpha-Methyltyrosine; D012110:Reserpine