DIFFERENTIAL-EFFECTS OF ALPHA(2)-ADRENOCEPTOR AGONISTS ON MIGRATING MOTOR COMPLEXES IN HEALTHY-VOLUNTEERS - STIMULATION BY CLONIDINE AND INHIBITION BY OXYMETAZOLINE

Objective: To analyse the effect of clonidine and oxymetazoline on mot ility of the small intestine in 16 healthy human volunteers. Design an d method: The migrating motor complex (MMC) of a duodenojejunal segmen t was monitored using a tube with water-perfused side holes connected to a pneumohydraulic system. Continuous 8-h recordings were obtained f rom each volunteer after a 12-h fast. In all experiments, saline was g iven as control for the first 4-h period and alpha2-adrenoceptor agoni sts for the remaining 8 h. In separate control studies, saline was giv en for the whole 8-h period. Results: Clonidine (150 mug/h) increased the number of MMCs from 2 (0-3) in controls to 3 (3-6) during the clon idine infusion (P < 0.05). Oxymetazoline (600 mug/h) profoundly reduce d all intestinal motor activity. The number of MMCs diminished from 3 (2-5) to 1 (0-1) during the oxymetazoline infusion (P < 0.05). Saline alone had no effect on motor activity. Conclusions: Oxymetazoline inhi bits MMCs in the human proximal small intestine, while clonidine activ ates them. This difference may be because oxymetazoline acts periphera lly, while clonidine acts in both the peripheral and the central nervo us systems. Our findings show, in accordance with animal studies, that alpha2-adrenoceptors are of importance in the control of motor activi ty of the human small intestine.