THE ACTIONS OF 5‐HYDROXYTRYPTAMINE AND HISTAMINE ON THE ISOLATED ILEUM OF THE TREE SHREW (<i>Tupaia glis</i>)

Abstract

Contractions to 5‐hydroxytryptamine (5‐HT) and histamine of longitudinal muscle from the isolated ileum of the tree shrew ( Tupaia ), guinea‐pig and rat were investigated by constructing dose‐response curves and studying the effects of various antagonists. In the Tupaia and rat ileum the contraction to 5‐HT was reduced by methysergide but not affected by tetrodotoxin (TTX), morphine, hexamethonium (C 6 ) or atropine. The response of guinea‐pig ileum to 5‐HT was not significantly inhibited by methysergide or C 6 , but was blocked by TTX, morphine and atropine. Histamine‐induced contraction of Tupaia and guinea‐pig ileum was antagonized by diphenhydramine but not by TTX, morphine, C 6 or atropine. Histamine was almost without effect on the rat ileum.