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Evidence for more than one type of 5‐hydroxytryptamine receptor in the human colon

The actions of methysergide, a 5‐hydroxytryptamine (5‐HT) antagonist, have been examined on muscle strips taken from the circular and longitudinal layers of the human colon. Relaxations of the longitudinal muscle to 5‐HT were antagonized by concentrations of methysergide known to be selective. Relaxations of the circular muscle to 5‐HT were unaffected by similar concentrations of methysergide. Responses of both types of muscle to 5‐HT were partially reduced by tetrodotoxin. Furthermore there was evidence for 5‐HT receptors in circular colonic muscle which were unaffected either by selective concentrations of methysergide or tetrodotoxin.