Functional evidence for a 5-HT sub(2B) receptor mediating contraction of longitudinal muscle in human small intestine

Application of 5-hydroxytryptamine induces contraction of longitudinal muscle strips from human terminal ileum. The response was resistant to antagonism by ketanserin, ondansetron or DAU6285, but was non-surmountably antagonized by methysergide. The selective 5-HT sub(2B/2C) receptor antagonist, SB 200646A evoked a concentration-dependent, parallel and dextral displacement of the concentration-response curve to 5-HT, yielding a pA sub(2) estimate of 7.17. Application of yohimbine, a 5-HT sub(1) and 5-HT sub(2B) receptor antagonist, also induced a rightward shift of the response curve to 5-HT, yielding a pA sub(2) estimate of 8.10. In conclusion, it appears that a 5-HT sub(2B) receptor mediates the contractile response of the longitudinal muscle of human small intestine to 5-HT.