Adrenoceptors and Colocolonic Inhibitory Reflex

The colocolonic inhibitory reflex ischaracterized by inhibition of proximal colonic motilityinduced by distal colonic distension. The aim of thisstudy was to investigate the underlying neuralmechanisms of this reflex, in vivo , using an isolatedloop of canine colon. In five beagle dogs, motility wasrecorded from an exteriorized colonic loop via a serosalstrain gauge connected to a digital data logger and chart recorder. Inflation of a balloon inthe distal colon resulted in inhibition of motility inthe isolated loop. Inhibition of motor activitypersisted following injection of propranolol (100g/kg intravenously), a -adrenoceptorantagonist, but was abolished following administrationof the ₂-adrenoceptor antagonistyohimbine (200 g/kg intravenously). This studyconfirms that the colocolonic inhibitory reflex is mediatedvia the extrinsic nerves to the colon. As the reflex wasabolished by ₂-, but not-adrenoceptor blockade, this indicates that thereflex pathway involves₂-adrenoceptors.