title: Inhibition of 5-carboxamidotryptamine-induced relaxation of guinea-pig ileum correlates with [125I]LSD binding.
abstract: 5-Hydroxytryptamine (5-HT), 5-carboxamidotryptamine (5-CT), 8-OH-DPAT and RU 24969 relax the guinea-pig ileum precontracted with histamine. This relaxation was characterized using 5-CT as agonist with a series of 8 competitive antagonists. [125I]LSD binding was measured in a membrane preparation of the longitudinal muscle of the guinea-pig ileum in the presence of 3 X 10(-7) M cinanserin in order to suppress binding to 5-HT2 receptors. There was a significant correlation (P less than 0.01) between the antagonism of 5-CT-induced relaxation (pA2 values) and the affinity values of the antagonists for [125I]LSD binding (pKD values). It was also shown that 5-CT relaxed histamine-precontracted longitudinal muscle strips of the guinea-pig ileum. The results suggest that the 5-HT receptor-mediating relaxation in the guinea-pig ileum can be labelled with [125I]LSD and that this receptor does not belong to the 5-HT2, 5-HT1A, 5-HT1B or 5-HT1C receptor subtypes.
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D005260:Female; D006168:Guinea Pigs; D007082:Ileum / Q000187:drug effects; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009126:Muscle Relaxation / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects*; D011985:Receptors, Serotonin / Q000187:drug effects*; D012701:Serotonin / Q000031:analogs & derivatives* / Q000494:pharmacology; D012702:Serotonin Antagonists
chemical_list: C031182:LSD receptor; D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; D012701:Serotonin; C047087:5-carboxamidotryptamine