PHARMACOLOGY OF 5-HYDROXYTRYPTAMINE RECEPTORS IN FROG-SKIN EPITHELIUM

5‐Hydroxytryptamine (5‐HT) stimulates active sodium transport and decreases the passive mucosal to serosal chloride permeability across frog skin. The relative importance of the different regions of the 5‐HT molecule in the mediation of these responses has been studied using a range of structurally related compounds. Substitution in the ethyl amine side chain of 5‐HT (5‐hydroxytryptophan) results in decreased receptor affinity and intrinsic activity; removal of the side chain (5‐hydroxyindole) abolishes activity. Methoxy substitution of the 5‐OH moiety of 5‐HT has no effect on intrinsic activity but reduces affinity; displacement of the hydroxyl group to position 6 diminishes intrinsic activity and affinity. It is concluded that both of the 5‐HT‐induced physiological effects are mediated via a single receptor which is distinct from α‐ and β‐adrenoceptors. 1979 British Pharmacological Society