Intestinal Motor Inhibition by Parasympathetic Drugs

Abstract

It was noted by Bernheim 1 that relaxation usually occurred when pilocarpine was added to a strip of guinea pig intestine contracted by histamine. This was confirmed 2 and several instances were noted in which abrupt relaxation occurred when pilocarpine was added to a strip of guinea pig intestine contracted by physostigmine. We found also that in most instances when the intestine was tonically contracted by pilocarpine, it was relaxed by physostigmine. This result was obtained in 4 of 7 trials using the duodenum and jejunum. The investigation has been extended to other parasympathetic drugs using the same method, viz., suspension of the strip in Ringer's solution.

On adding pilocarpine to the bath containing an intestinal strip contracted by acetyl choline, we obtained relaxation of the duodenum, jejunum, ileum, proximal, mesial, and distal colon. In only 3 of the 66 trials was a motor effect produced by the subsequent addition of the second parasympathetic drug (pilocarpine). This effect is only occasionally reversible, that is, acetyl choline relaxes the intestine contracted by pilocarpine only in a minority of the trials. In each intestinal strip tested acetyl choline caused a considerable tonic contraction and the increased tonus was usually maintained.

In the case of the esophagus and cardia, Carlson, Boyd and Pearcy 3 suggest that the inhibition resulting from direct or reflex stimulation of the vagus nerve is due to the existing state of tonus. While this hypothesis would explain some of our results, a great many of them are not consistent with it, and we are forced to conclude that another factor is involved. We are continuing these experiments to obtain further data.