Selective and functional 5‐hydroxytryptamine4 receptor antagonism by SB 207266

• Published in: British journal of pharmacology 1996-06, Vol.118 (3), p.665-670
• Main Authors: Wardle, K.A., Bingham, S., Ellis, E.S., Gaster, L.M., Rushant, B., Smith, M.I., Sanger, G.J.
• Format: Article
• Language: English
• Subjects: 5‐HT (5‐hydroxytryptamine, serotonin); 5‐HT4 receptor; amide; Animals; Benzimidazoles - pharmacology; Bridged Bicyclo Compounds, Heterocyclic - pharmacology; Colon - drug effects; Dogs; Dose-Response Relationship, Drug; Guinea Pigs; Indoles - pharmacology; Male; Muscle Contraction - drug effects; orally active; Piperidines - pharmacology; SB 207266; Serotonin - pharmacology; Serotonin Antagonists - pharmacology; Time Factors
• ISSN: 0007-1188; 1476-5381
• DOI: 10.1111/j.1476-5381.1996.tb15452.x

1 The pharmacology of a novel 5‐HT4 receptor antagonist, SB 207266 has been evaluated in vitro in the guinea‐pig distal colon longitudinal muscle myenteric plexus (LMMP) and in vivo in the dog Heidenhain pouch. 2 SB 207266 is a highly potent antagonist of 5‐HT‐evoked, cholinergically‐mediated contractions in the guinea‐pig distal colon. Low concentrations (0.1–10 nM) produced a parallel shift to the right of the concentration‐effect curve (apparent pA2 10.6±0.1) with no significant effect on the maximum response. With higher concentrations of SB 207266 (30 nM and above) the maximum response to 5‐HT was reduced. 3 The antagonism seen with SB 207266 cannot be attributed to a non‐selective effect since high concentrations (1 μm) had no effect on cholinergically‐mediated contractions evoked by the nicotinic receptor agonist DMPP in the same preparation. 4 SB 207266 is not an irreversible antagonist since the effects of the compound were reversible upon washing of the tissue. 5 In the dog Heidenhain pouch, oral (0.1–100 μg kg−1) and intravenous (0.1–100 μg kg−1) administration of SB 207266 produced a dose‐dependent antagonism of the contractions evoked by a bolus intravenous injection of 5‐HT. An ID50 for SB 207266 of 1.3 μg kg−1 was obtained following i.v. administration and 9.6 μg kg−1 following oral administration. 6 The antagonistic effects of SB 207266 (0.1–100 μg kg−1) in the dog Heidenhain pouch were long lasting since, following oral administration, the response to 5‐HT was reduced for at least 135 min. 7 SB 207266 is a highly potent, highly selective and orally active 5‐HT4 receptor antagonist. This compound is the first orally active amide to be identified in this class of antagonists and as such is an important new tool in the evaluation of 5‐HT4 receptor function both in vitro and in vivo.