Effect of synthetic oxytocin on the motor and bioelectrical activity of the stomach and small intestines (in vivo).

A study is made of the effect of synthetic oxytocin on the mechanograms and electromyograms of the stomach and small intestines of 11 wakeful and 7 chloralose-anaesthesized dogs. Oxytocin was administered intravenously in doses of 0.5 to 2.0 IU/kg for the anaesthesized dogs. The mechanograms were recorded by means of the balloon-kymographic method, the electromyograms-by silver macroelectrodes implanted in the muscle wall. In all animals oxytocin decreased the tone and abolished the peristaltic contractions and the spike-potentials in the stomach and in the intestines for 8 to 15 min. This effect of oxytocin is not eliminated by adreno-, cholino- and gangliolytics. Besides these changes, oxytocin administered in wakeful dogs reduces two or three times the frequency of the basic electric rhythm (BER) in the stomach from 10 s to 3 min and increases the propagation of BER in the small intestine from 10 s to 10 min. The effect of oxytocin on gastric and intestinal BER is eliminated by cholinolytics and gangliolytics and it is not manifested in the small pouch of Heindenhein. A direct myogenic mechanism of oxytocin effect on the activity of the gastro-intestinal smooth muscle is discussed, as well as the effect mediated by vagal nerves and cholinergic receptors.