SB 204070

Antagonism by SB 204070 of 5-HT-evoked contractions in the dog stomach: an in-vivo model of 5-HT4 receptor function.[Pubmed:7602484]

J Pharm Pharmacol. 1995 Mar;47(3):219-22.

The ability of 5-hydroxytryptamine (5-HT) to evoke contractile activity in the gastric Heidenhain pouch was measured in conscious dogs using a method in which 5-HT4 receptor-antagonist activity can be measured in-vivo. At doses of 5-HT which evoked short-lived measurable responses (5 or 10 micrograms kg-1, i.v.), it was found that this activity was greatly reduced by atropine (100 micrograms kg-1, i.v.), but was unaffected by methysergide, methiothepin, ketanserin (each at 100 micrograms kg-1, i.v.) or granisetron (10 or 100 micrograms kg-1, i.v.). At best SDZ 205-557 2-diethylaminoethyl-[2-methoxy-4-amino-5-chloro] benzoate; 100 micrograms kg-1, i.v.) reduced the action of 5-HT in 4/5 animals and increased it in the other but its effects were variable in magnitude and not consistently maintained. However, the more potent and selective 5-HT4-receptor antagonist SB 204070 (1-butyl-4-piperidinylmethyl 8-amino-7-chloro-1, 4-benzodioxan-5-carboxylate hydrochloride) dose-dependently antagonized the 5-HT-evoked contractions in all dogs tested. This action was reversible, but long-lasting with an effective half-life of 18.0h when administered at 1 microgram kg-1. The estimated ID50 value was 0.55 microgram kg-1.

The effects of SB 204070, a highly potent and selective 5-HT4 receptor antagonist, on guinea-pig distal colon.[Pubmed:7921604]

Br J Pharmacol. 1994 Jul;112(3):789-94.

1. The pharmacology of a novel 5-HT4 receptor antagonist, SB 204070 has been evaluated in the guinea-pig isolated distal colon longitudinal muscle-myenteric plexus (LMMP). 2. SB 204070 is a highly potent antagonist of 5-HT-evoked cholinergically-mediated contractions in the guinea-pig distal colon. Low concentrations (10-100 pM) produced a shift to the right of the curve (apparent pA2 10.8 +/- 0.1) with no significant effect on the maximum response. With higher concentrations of SB 204070 (300 pM and above), the maximum response to 5-HT was reduced. 3. When tested against the partial 5-HT4 receptor agonist, BIMU 1, SB 204070 was active at similar low concentrations (10 pM and above) but produced a reduction in maximum, with no prior shift to the right of the curve, at all concentrations tested (10-300 pM). 4. The antagonism seen with SB 204070 is unlikely to be due to a non-selective effect since high concentrations (10 nM and 1 microM) of the compound had no effect on cholinergically-mediated contractions evoked by the nicotinic receptor agonist, DMPP, in the same preparation. SB 204070 is unlikely to be an irreversible antagonist since the effects of the compound could be reversed upon washing of the tissue. 5. Radioligand binding studies show that SB 204070 has a greater that 5000 fold selectivity for the 5-HT4 receptor over 5-HT1A, 5-HT1D, 5-HT1E, 5-HT2A, 5-HT2C, 5-HT3, GABAA, BDZ, TBPS, A1 adenosine receptors, alpha 1, alpha 2, beta 1, beta 2 adrenoceptors and D1, D2 and D3 dopamine receptors. 6. SB 204070 is a highly potent, highly selective 5-HT4 receptor antagonist and as such is an important new tool in evaluating the functional role of the 5-HT4 receptor.

An improved in vitro bioassay for the study of 5-HT(4) receptors in the human isolated large intestinal circular muscle.[Pubmed:10780964]

Br J Pharmacol. 2000 Apr;129(8):1601-8.

Recently, it was demonstrated that 5-HT induces relaxation of human colon circular muscle through activation of 5-HT(4) receptors and 5-HT(7) receptors. The aim of the current study was to develop a new in vitro bioassay of human colon that would facilitate the pharmacological analysis of 5-HT responses mediated solely by 5-HT(4) receptors. Contracting circular muscle strips with KCl (80 mM) yielded a stable contractile tension and, in contrast to muscarinic cholinoceptor agonists and histamine, a profound reduction of spontaneous contractility. This allowed the establishment of reproducible, fully-defined, agonist concentration-response curves by cumulative dosing. Under these conditions, 5-HT induced a concentration-dependent relaxation (pEC(50) 7.31, Hill slope 0.91). Neither methysergide (10 microM) nor granisetron (1 microM) affected the 5-HT-induced relaxation, suggesting that 5-HT(1), 5-HT(2), 5-HT(3), 5-ht(5), 5-HT(6) or 5-HT(7) receptors are not involved. The lack of effect of tetrodotoxin (0.3 microM) indicated a direct effect of 5-HT on the smooth muscle. The selective 5-HT(4) receptor antagonists GR 113808, GR 125487 and RS 39604 competitively antagonized the 5-HT-induced relaxation (pK(B) 9.43, 10.12 and 8.53, respectively). SB 204070 (1 nM) produced a rightward shift (pA(2) 10.34) and depression of the 5-HT curve. These affinity estimates are similar to those previously reported for 5-HT(4) receptors. The selective 5-HT(4) receptor agonists, prucalopride and R076186, induced relaxations (pEC(50) 7.50 and 7.57, respectively), that were blocked by GR 113808 (3 nM), yielding pA(2) estimates of 9.31 and 9.21, respectively. To summarise, in KCl (80 mM)-contracted muscle strips, 5-HT induces relaxation through activation of a homogeneous smooth muscle 5-HT(4) receptor population. This new bioassay allows the focused, pharmacological characterization of human colonic 5-HT(4) receptors in vitro.