A non-selective beta-blocker, bopindolol, exhibits high affinity to 5-HT1A receptor subtype in rat brain as assayed by competition binding experiments

This study investigated the displacement potencies of bopindolol and its two metabolites (18-502 and 20-785) for H-3-serotonin (5-HT), H-3-8-OH-DPAT, H-3-ketanserin, H-3-mesulergine, H-3-GR65630 bindings to various 5-HT1, 5-HT1A, 5-HT1B, 5-HT1D, 5-HT2C, 5-HT3 receptor subtypes in the rat brain using the radioligand binding assay method. Scatchardplots of these radioligands exhibited high affinities and exhibited a single class of binding sites. Bopindolol and its metabolites for only the 5-HT1A receptor showed high pKi values, although low values to other 5-HT subtypes were observed. The rank order of affinity potencies of bopindolol and its metabolites against 5-HT1A receptors as assessed with pKi values were 18-502 > bopindolol > 20-785. By contrast, propranolol also showed high affinity to 5-HT1B in addition to 5-HT1A. Thus, these findings suggest that bopindolol and its two metabolites have high potential affinity to 5-HT1A subtype, implying that these drugs are more selective to 5-HT receptor subtypes than propranolol and that bopindolol may in part contribute to the pharmacological function through to 5-HT1A receptor subtype.