Adrenoceptors and colocolonic inhibitory reflex

The colocolonic inhibitory rifler is characterized by inhibition of proxima l colonic motility induced by distal colonic distension. The aim of this st udy was to investigate the underlying neural mechanisms of this reflex, in vivo, using an isolated loop of canine colon. In five beagle dogs, motility was recorded from an exteriorized colonic loop via a serosal strain gauge connected to a digital data logger and chart recorder. Inflation of a ballo on in the distal colon resulted in inhibition of motility in the isolated l oop. Inhibition of motor activity persisted following injection of proprano lol (100 mu g/kg intravenously), a beta-adrenoceptor antagonist, hut was ab olished following administration of the alpha(2)-adrenoceptor antagonist yo himbine (200 mu g/kg intravenously). This study confirms that the colocolon ic inhibitory reflex is mediated via the extrinsic nerves to the colon, As the reflex was abolished by alpha(2)-, but not beta-adrenoceptor blockade, this indicates that the reflex pathway involves alpha(2)-adrenoceptors.