Inhibition of stress‐stimulated colonic propulsion by α2‐adrenoceptor antagonists in rats

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Abstract
Alpha2‐adrenoceptor antagonists have been reported to stimulate colonic motor activity, but the effect on colonic motor dysfunction is unclear. We have investigated the effect of α2‐adrenoceptor antagonists on wrap‐restraint stress‐stimulated and normal colonic propulsion in rats. Colonic propulsion was evaluated by the transit of a charcoal marker along the colon. Faecal pellets output was also measured. A 30‐min exposure to wrap‐restraint stress starting 120 min after infusion of the charcoal marker significantly stimulated colonic transit with a concomitant increase in faecal pellets. Yohimbine and idazoxan, α2‐adrenoceptor antagonists, clonidine, an α2‐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 only weakly inhibited faecal excretion. Neither α2‐adrenoceptor antagonists nor atropine had any significant effect on normal colonic transit, whereas clonidine and the 5‐HT3 receptor antagonists inhibited it. α2‐Adrenoceptor antagonists as well as clonidine, atropine and 5‐HT3 receptor antagonists inhibit the stress‐induced colonic motor dysfunction in rats.