On the Motility of the Colon of the Dog

Abstract

A new technique was devised, for the purpose of studying separately the movements of the 2 coats of the intestine of the unanesthetized dog. The results obtained necessitate a revised statement of the “Law of the Intestine”, at least for the colon of the dog.

A section of the colon about 10 cm. long was exteriorized; opened along its anti-mesenteric border, and grafted onto the subcutaneous tissue of the anterior abdominal wall. The mucosal surface now presents outward, so that stimuli may be applied to it in imitation of intra-colonic conditions. The motility of the coats of the graft is recorded by modified enterograph levers. The principle involved is that of recording the change in distance between two clips attached to the mucosa, either longitudinally or transversely to the graft.

The stimulus which was used in the present study was a stroke applied to the mucosa by means of a blunt metal teaser. The experiments were performed on non-anesthetized animals, after they had recovered from the operation, and had been trained to lie quietly on their sides.

Longitudinal irritation of the mucosa of the colon graft elicited contraction of the longitudinal muscle, with little or no responce from the circular muscle. Irritation of the mucosa transversely elicits a response from both coats of the colon. The longitudinal muscle contracts first, and is followed by contraction of the circular muscle. The biological significance of this order of contraction?s made evident by the following observations.

When the transverse stroke stimulus is applied to the mucosa cephalad to the recording clips, the longitudinal muscle contracts at and below the area of stimulation; there is no contraction above the stimulus. The circular muscle contracts at and above the area of stimulation; there is no contraction below. The longitudinal contraction below the stimulus precedes the circular contraction above the stimulus by 3 to 5 seconds. The “myenteric reflex” is abolished by atropine given systemically, and by cocaine applied to the mucosa of the graft at the area of stimulation.

Contraction of the longitudinal muscle, acting alone, enlarges the lumen of the gut. When this occurs below the point of stimulation, the downward passage of the bolus is facilitated.

Contraction of the circular muscle, acting alone, narrows the lumen of the gut. When this occurs above the stimulus, the passage of the bolus orad is prevented. Occurring after the gut lumen is enlarged below the bolus, it promotes the downward passage of the bolus. As the bolus passes downward, a new area is stimulated, and new reflexes are initiated. Such a sequence of reflex responses may give the appearance of peristalsis.