A NONSELECTIVE 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 i ts 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 var ious 5-HT1, 5-HT1A, 5-HT1B, 5-HT1D, 5-HT2C, 5-HT3 receptor subtypes in the rat brain using the radioligand binding assay method. Scatchardpl ots of these radioligands exhibited high affinities and exhibited a si ngle class of binding sites. Bopindolol and its metabolites for only t he 5-HT1A receptor showed high pKi values, although low values to othe r 5-HT subtypes were observed. The rank order of affinity potencies of bopindolol and its metabolites against 5-HT1A receptors as assessed w ith pKi values were 18-502 > bopindolol > 20-785. By contrast, propran olol also showed high affinity to 5-HT1B in addition to 5-HT1A. Thus, these findings suggest that bopindolol and its two metabolites have hi gh potential affinity to 5-HT1A subtype, implying that these drugs are more selective to 5-HT receptor subtypes than propranolol and that bo pindolol may in part contribute to the pharmacological function throug h to 5-HT1A receptor subtype.