5-HT1D and 5-HT2B receptors mediate contraction of smooth muscle in human small intestine.

In conclusion, 5-HT has been shown to contract both circular and longitudinal muscle layers of human terminal ileum. By the use of selective antagonists, the receptors mediating these actions have been identified. In the circular muscle of human small intestine, 5-HT-induced contraction is mediated via a receptor of the 5-HT1D sub-type, whereas a receptor of the 5-HT2B sub-type mediates the contractile response to 5-HT of longitudinal muscle layers.