Abstract

Isolated loops of dog ileum were perfused at constant blood flow. The intraarterial injection of acetylcholine produced an initial increase in intestinal vascular resistance which coincided with contraction of the intestinal musculature. The constrictor effect was followed by a sustained dilator response. The initial constrictor response is probably not the result of the liberation of catecholamines by acetylcholine since it was unchanged or exaggerated in animals pretreated with reserpine. Atropine abolished both the intestinal contraction and the constrictor response elicited by acetylcholine. Intestinal contraction which compresses or distorts the vessels lying within the wall appeared to be the mechanism of the increase in resistance. Determination of segmental resistance changes revealed that the major alteration of vessel caliber occurred in the small vessel portion of the isolated loop. Evidence was presented which revealed that the intestinal sympathetic innervation does not include cholinergic fibers.