CLONIDINE DELAYS SMALL INTESTINAL TRANSIT IN THE RAT

Abstract

Clonidine [CD] (0.01-1.0 mg/kg s.c.) delayed small intestinal [SI] transit but not gastric emptying in the unanesthetized rat, with a maximal effect seen at 0.1 mg/kg. Gastric emptying was expressed as the percentage of intragastrically administered 51Cr emptied into the SI after 45 min. SI transit was the percentage of the SI length traveled 45 min after oral or duodenal administration of black ink. The depression of SI transit by CD to 20-30% of control values was blocked by phentolamine and yohimbine, but not by prazosin or phenoxybenzamine, suggesting a presynaptic (.alpha.-2) agonist action of CD. Pretreatment of rats with 6-hydroxydopamine, propranolol, atropine, methysergide, naloxone, mepyramine or metiamide failed to alter the effects of CD. Apparently, an .alpha.-adrenergic receptor, possibly presynaptic, regulates small bowel propulsion in rat without involvement of acetylcholine, norepinephrine, endorphins, histamine or serotonin.