A pharmacological analysis of the contractile action of histamine upon the ileal region of the isolated, blood-perfused small intestine of the rat.

1. The mode of action of histamine was investigated on the rat isolated small intestine perfused at a fixed flow rate through the superior mesenteric artery with blood from the carotid artery of a heparinized donor rat. Compounds were closely injected into the superior mesenteric artery. 2. Increasing doses (1 to 100 micrograms) of histamine caused a monophasic fast contraction of the ileum. 3. The fast contraction was abolished by tetrodotoxin, hexamethonium, morphine or mepyramine, but was not prevented by atropine. 4. The present study indicates that histamine produces the fast contraction of the ileum by primarily acting on the myenteric nerve plexus involving cholinergic interneurones.