Inhibition of stress-stimulated colonic propulsion by alpha(2)-adrenoceptor antagonists in rats

Alpha2-adrenoceptor antagonists have been reported to stimulate colonic mot or activity, but the effect on colonic motor dysfunction is unclear. We hav e investigated the effect of alpha(2)-adrenoceptor antagonists on wrap-rest raint stress-stimulated and normal colonic propulsion in rats. Colonic prop ulsion was evaluated by the transit of a charcoal marker along the colon. F aecal pellets output was also measured. A 30-min exposure to wrap-restraint stress starting 120 min after infusion of the charcoal marker significantl y stimulated colonic transit with a concomitant increase in faecal pellets. Yohimbine and idazoxan, alpha(2)-adrenoceptor antagonists, clonidine, an a lpha(2)-adrenoceptor agonist, and atropine suppressed wrap-restraint stress -stimulated colonic transit and faecal excretion in a dose-dependent manner . Ondansetron and YM060, 5-hydroxytryptamine3 (5-HT3) receptor antagonists, potently inhibited wrap-restraint stress-stimulated colonic transit, but o nly weakly inhibited faecal excretion. Neither alpha(2)-adrenoceptor antago nists nor atropine had any significant effect on normal colonic transit, wh ereas clonidine and the 5-HT3 receptor antagonists inhibited it. alpha(2)-a drenoceptor antagonists as well as clonidine, atropine and 5-HT3 receptor a ntagonists inhibit the stress-induced colonic motor dysfunction in rats.