Effect of cooling, local anaesthetic compounds and botulinum toxin on the responses of and the acetylcholine output from the electrically transmurally stimulated isolated guinea-pig ileum.

Electrical transmural stimulation of the isolated guinea-pig ileum preparation which was distended by an intraluminal pressure insufficient to elicit peristalsis produced two effects, one a longitudinal contraction and the other an emptying response brought about by a co-ordinated propagated contraction of the circular muscle. The parameters of the electrical stimulus used were such that these effects were probably produced by stimulation of the nervous plexuses in the wall of the ileum. In the presence of the anticholinesterase NN-diisopropylphosphodiamidic fluoride (Mipafox), acetylcholine was detected in the fluid passing through the lumen and also in the fluid in the organ bath. The amount was increased after a period of electrical stimulation. As variation of the frequency of stimulation from 5/min to 25/sec did not alter statistically significantly the acetylcholine output, a frequency of 5/min was used. Cooling to 13 degrees C, the effect of local anaesthetic compounds and botulinum toxin reduced both the emptying response and longitudinal contractions of the ileum which followed transmural stimulation, with a concurrent reduction in acetylcholine output. It was concluded that the acetylcholine was released by electrical transmural stimulation from the intramural nerve plexuses in the wall of the guinea-pig ileum.