Development of a radioligand binding assay for 5‐HT₄ receptors in guinea‐pig and rat brain

Abstract

1 The 5-HT4 receptor antagonist, GRI13808, has been radiolabelled to a high specific activity with tritium. antagonists acting at the 5-HT4 receptor but not by compounds selective for other 5-HT receptors or other neurotransmitter receptors. 5 Autoradiographic analysis revealed a discrete localization in both guinea-pig and rat brain with high concentrations of binding in brain areas such as the striatum, substantia nigra and olfactory tubercle. 6 [3H]-GR113808 binding to homogenates of guinea-pig striatum meets the criteria for labelling of the 5-HT4 receptor and, as such, represents the first characterization of this receptor in a radioligand binding assay.

Pharmacological characterization of two novel and potent 5‐HT4 receptor agonists, RS 67333 and RS 67506, in vitro and in vivo

“…Concentration-ratios were measured at the agonist concentration that elicited 30% of the maximal relaxation, since under some conditions the effects at higher concentrations may have reflected muscarinic receptor antagonism. The apparent affinity (pKB) of GR 113808, a potent and selective 5-HT4 receptor antagonist (Grossman et al, 1993;Gale et al, 1994), determined against responses to each agonist, estimated using a single concentration of antagonist (10 nM).…”

RS 23597‐190: a potent and selective 5‐HT4 receptor antagonist

“…These include LY297582 (Krushinski et al, 1992), SB 203186 (Kaumann et al, 1992b and GR 113808 (Grossman et al, 1992). LY297582 is structurally similar to RS 23597-190, although the selectivity between rat oesophageal 5-HT4 receptors and guinea-pig ileal 5-HT3 receptors is lower (240 fold).…”

“…LY297582 is structurally similar to RS 23597-190, although the selectivity between rat oesophageal 5-HT4 receptors and guinea-pig ileal 5-HT3 receptors is lower (240 fold). GR 113808 is structurally different, has a notably higher affinity for the 5-HT4 receptor (pA2 = 9.2-9.5; Grossman et al, 1992) than RS 23597-190 and has formed the basis of a radioligand binding assay. However, it is also an ester, with a very short plasma half-life (Grossman et al, 1992).…”

“…GR 113808 is structurally different, has a notably higher affinity for the 5-HT4 receptor (pA2 = 9.2-9.5; Grossman et al, 1992) than RS 23597-190 and has formed the basis of a radioligand binding assay. However, it is also an ester, with a very short plasma half-life (Grossman et al, 1992). SC-63606 , by contrast, is more stable in vivo but is less selective (8 fold) than RS 23597-190 for the 5-HT4 receptor over 5-HT3 receptors.…”

Azaadamantane benzamide 5-HT4 agonists: gastrointestinal prokinetic SC-54750

“…Benzamide coupling of the aminoazaadamantanes with 4-amino-5-chloro-2-methoxy benzoic acod 8 utilizing carbonyldiimidazole (CDI) as the coupling reagent gave the requisite aminoazaadamantane benzamides which were treated with hydrogen chloride to afford the crystalline monohydrochloride salts 9a-d (Scheme 3). As seen in Table 1, anti-aminoazaadamantane 9b is twice as potent as the corresponding synisomer 9a in 5-HT 4 agonism in the rat tunica muscularis mucosae (TMM) assay, 23 and the antiisomer is an order of magnitude more potent in 5-HT 4 receptor binding 24 (Ki = 57 nM vs. > 500 nM). Anti-aminoazaadamantane 9b is also substantially (37X) more potent than the syn-isomer in 5-HT 3 binding.…”