Studies in vivo of the ileocaeco-colic sphincter in the cat and dog.

EDITORIAL SYNOPSiS A study of the response of the ileocaeco-colic sphincter2 of the cat and dog to sympathomimetic and parasympathomimetic drugs and to stimulation of the autonomic nerves is reported. The response to drugs in vivo is identical with that previously noted in vitro, namely, contraction of the sphincter by adrenaline, noradrenaline, and acetylcholine, and relaxation by isoprenaline. Stimulation of the sympathetic nerves consistently resulted in contraction of the sphincter, but stimulation of the parasympathetic nerves (vagus) sometimes resulted in contraction and at other times relaxation of the sphincter. In view of the presence of P receptors in the sphincter, which, when stimulated cause relaxation of the muscle, it is suggested that the vagus contains adrenergic nerves which supply these receptors.