Central α2‐Adrenergic Control of Colonic Transit in Rats

Abstract

The effects of central and peripheral administration of α2‐adrenoceptor agonists on colonic propulsion were examined in conscious rats chronically fitted with a catheter inserted in the lumen of the proximal colon and a cannula placed in a cerebral lateral ventricle. The mean retention time of a marker in the colon was determined by administration of a bolus of [51Cr]sodium chromate into the proximal colon and collection of the feces at hourly intervals. In control studies the colonic mean retention time was 7.5 ± 1.6 hours. Clonidine administered intraperitonedy or intracerebroventricularly produced a dose‐dependent increase in mean retention time but was more potent when given intracerebroventricularly. St‐91, a quaternary derivative of clonidine which poorly crosses the blood‐brain barrier, delayed colonic transit after intracerebroventricular, but not after intraperitoneal, administration at the same dose. The increase in colonic mean retention time induced by intraperitonedy administered clonidine was antagonized by intracerebroventricular administration of yohimhine but not of prazosin, an α1‐adrenoceptor antagonist. Yohimbine intracerebroventricularly or intraperitonedy administered alone at the same dose accelerated the colonic transit. Such data suggest a possible role of central α2‐adrenoceptors in the regulation of colonic motility in rats.