Effects of selective h5-HT1B (SB-216641) and h5-HT1D (BRL-15572) receptor ligands on guinea-pig and human 5-HT auto- and heteroreceptors

Abstract

Human cerebral cortical slices and synaptosomes, guinea-pig cerebral cortical slices and human right atrial appendages were used to study the effects of SB-216641, a preferential h5-HT1B receptor ligand, and of BRL-15572, a preferential h5-HT1D receptor ligand, on the presynaptic h5-HT1B and h5-HT1B-like autoreceptors in the human and guinea-pig brain preparations, respectively, and on the presynaptic h5-HT1D heteroreceptors in the human atrium. The brain preparations, preincubated with [3H]serotonin ([3H]5-HT), and the segments of atrial appendages, preincubated with [3H]noradrenaline, were superfused with modified Krebs' solution and tritium overflow was evoked electrically (human and guinea-pig cerebral cortex slices and human atrial appendages) or by high K+ (human cerebral cortex synaptosomes). The electrically evoked tritium overflow from guinea-pig cerebral cortex slices was reduced by the 5-HT receptor agonist 5-carboxamidotryptamine (5-CT). This effect was not modified by BRL-15572 (2 microM; concentration 154 times higher than its Ki at h5-HT1D receptors) but was antagonized by SB-216641 (0.1 microM; concentration 100 times higher than its Ki at h5-HT1B receptors; apparent pA2 8.45). SB-216641 (0.1 microM) by itself facilitated, whereas BRL-15572 (2 microM) did not affect, the evoked overflow. In human cerebral cortex slices SB-216641 (0.1 microM) also facilitated, and BRL-15572 (2 microM) again failed to affect, the electrically evoked tritium overflow. In human cerebral cortical synaptosomes, 5-CT reduced the K+-evoked tritium overflow. This response was unaffected by BRL-15572 (300 nM) but antagonized by SB-216641 (15 nM; drug concentrations 23 and 15 times higher than their Ki at h5-HT1D and h5-HT1B receptors, respectively). Both drugs, given alone, did not modify the K+-evoked tritium overflow. In human atrial appendages, the electrically evoked tritium overflow was inhibited by 5-HT in a manner susceptible to antagonism by BRL-15572 (300 nM; 23 times Ki at h5-HT1D receptors) but not by SB-216641 (30 nM; 30 times Ki at h5-HT1B receptors). Both drugs by themselves did not change the electrically evoked tritium overflow. In conclusion, SB-216641 behaves as a preferential antagonist at native human 5-HT1B receptors and BRL-15572 as a preferential antagonist at native human 5-HT1D receptors. These compounds are clearly useful tools for the differentiation between human 5-HT1B and 5-HT1D receptors in functional studies.

Molecular cloning, sequence analysis and pharmacological properties of the porcine 5‐HT1D receptor

“…The a nity constants of these 14 compounds obtained in the present experiments with the cloned porcine 5-HT 1D receptor showed a high correlation with those previously reported with the cloned human 5-HT 1D receptor ( Figure 5, . However, the most salient ®nding in the present investigation was that BRL15572, which behaves as a selective antagonist at the human 5-HT 1D receptor Schlicker et al, 1997), did not show high a nity at the porcine 5-HT 1D receptor. The profound implications of this ®nding are obvious; a ligand selectively recognizing a particular receptor may fail at other species' homologues.…”

“…Admittedly, this di erence was not as great using [ 3 H]-5-CT as ligand (r s =0.724 and 0.716, respectively; Figure 5, left panels). However, it is interesting to point out that the selective antagonist at the human 5-HT 1D receptor, BRL15572 Schlicker et al, 1997), displayed much less a nity at the pig 5-HT 1D receptor ( Figure 5, upper panels). As can be expected, the selective antagonist at the human 5-HT 1B receptor, SB224289 Selkirk et al, 1998), did not show a high a nity at the pig 5-HT 1D receptor ( Figure 5, lower panels).…”

“…, that have been shown to be selective antagonists for the human 5-HT 1B and 5-HT 1D receptors Schlicker et al, 1997;Gaster et al, 1998;Selkirk et al, 1998), respectively, it is di cult to be sure that these compounds also have a high and selective a nity at the respective porcine receptor.…”

SB‐224289–a novel selective (human) 5‐HT1B receptor antagonist with negative intrinsic activity

“…However both GR127935 and SB-216641 are partial agonists at recombinant h5-HT 1B receptors expressed in CHO cell lines, as is BRL-15572 at h5-HT 1D receptors. In native tissues no intrinsic activity has been observed with any of these compounds (Skingle et al, 1996;Schlicker et al, 1997) and they have been used as antagonists to characterize both serotonergic auto-and hetero-receptors (Roberts et al, 1996;Schlicker et al, 1997). Nonetheless, if these compounds were used in a system with receptor reserve or highly e cacious receptor-e ector coupling, they may display intrinsic activity.…”

Success and failure of triptans

“…Investigations in anaesthetised animals show that sumatriptan as well as other triptans exclusively decrease the arteriovenous anastomotic fraction of carotid blood flow [5,6]. The role of 5-HT 1B and 5-HT 1D receptors in the sumatriptan-induced constriction of porcine carotid arteriovenous anastomoses has been investigated by using SB224289 and BRL15572, which have a selective antagonist activity at cloned human 5-HT 1B and 5-HT 1D receptors, respectively [9][10][11]. SB224289, but not BRL15572 antagonises the effects of sumatriptan (Fig.…”