An inhibitory effect of acetylcholine on the response of the guinea-pig ileum to histamine

If small doses of histamine are alternated with small doses of acetylcholine on the isolated guinea-pig ileum in Tyrode solution, the response to histamine tends to diminish and may disappear. When the response to the small doses of histamine has disappeared, a contraction may be elicited by larger doses. The diminution is reversible, the response returning if the preparation is left unstimulated by drugs for varying periods of time. This phenomenon also occurs when the loops are suspended in Tyrode solution containing cocaine or atropine.

Some aspects of the pharmacology of an homologous series of choline esters of fatty acids

The pharmacological effects of a series of fatty acid-choline esters have been studied on the isolated rabbit heart, the isolated guinea-pig ileum and the rat stomach. The effect changed with increasing chain length, and three different types of response were observed. The shortchain compounds produced depression of the isolated rabbit heart and spasm of the isolated guinea-pig ileum. Only one, butyrylcholine, had an erratic stimulating effect on hydrochloric acid secretion by the partially vagotomized rat stomach. Medium-chain compounds had a stimulating effect on the isolated rabbit heart, a mixed spasmogenic and relaxant effect on the isolated guinea-pig ileum, and no effect on the rat stomach. Long-chain compounds blocked the effect of acetylcholine on the isolated rabbit heart and the isolated guinea-pig ileum; they also depressed spontaneous hydrochloric acid secretion by the rat stomach. The nature of these three types of response is discussed.

Assay of renin and hypertension with the isolated guineapig ileum

Renin and hypertensin may be easily assayed with the isolated guinea-pig ileum, which is as sensitive as the vascular toad preparation. Hypertensin itself is the substance which acts on the smooth muscle of the ileum.