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. 1993 Nov;110(3):1023–1030. doi: 10.1111/j.1476-5381.1993.tb13916.x

Characterization of the 5-HT4 receptor mediating tachycardia in piglet isolated right atrium.

A D Medhurst 1, A J Kaumann 1
PMCID: PMC2175817  PMID: 8298790

Abstract

1. In order to explore whether 5-HT4 receptor subtypes exist, we have characterized further the 5-HT4 receptor that mediates tachycardia in the piglet isolated right atrium. All experiments were carried out in the presence of propranolol (400 nM) and cocaine (6 microM). We used tryptamine derivatives, substituted benzamides and benzimidazolone derivatives as pharmacological tools. 2. Tachycardia responses to 5-hydroxytryptamine (5-HT) were mimicked by other tryptamine derivatives with the following order of potency: 5-HT > 5-methoxytryptamine alpha-methyl-5-HT = bufotenine bufotenine > 5-carboxamidotryptamine = tryptamine (after treatment with pargyline) > 5-methoxy-N,N-dimethyltryptamine > 2-methyl-5-HT. 3. The substituted benzamides were all partial agonists relative to 5-HT except (-)-zacopride which was a full agonist. The stimulant potency order was renzapride > cisapride = (-)-zacopride > metoclopramide > (+)-zacopride. 4. The benzimidazolone derivatives had contrasting effects. BIMU 8 (endo-N-(8-methyl-8-azabicyclo[3.2.1]oct-3-yl)-2,3-dihydro-(1-methyl(eth yl- 2-oxo-1H-benzimidazole-1-carboxamide hydrochloride) was a full agonist relative to 5-HT whilst BIMU 1 (endo-N-(8-methyl-8-azabicyclo[3.2.1]oct-3-yl)-2,3-dihydro-3-ethyl-2-oxo - 1H-benzimidazole-1-carboxamide hydrochloride) was a partial agonist with low intrinsic activity compared to 5-HT but had similar potency. We estimated a pKB of 7.9 for BIMU 1 antagonism of 5-HT-induced tachycardia.(ABSTRACT TRUNCATED AT 250 WORDS)

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Selected References

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