Serotonin 5‐HT1D Receptors

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Abstract
5-HT receptors are subdivided into 3 families, 5-HT1, 5-HT2, and 5-HT3, of which subtypes have been described. The 5-HT receptor field has experienced over the last 10 years a revival due to the availability of new and more selective drugs and new techniques. This communication deals essentially with the biochemical approaches to characterize 5-HT1D receptors, and their comparison with 5-HT1B receptors. The methods used include radioligand binding, in vitro autoradiography, and second messenger studies. 5-HT1 receptor subtypes are labeled with [3H]5-HT and present a large heterogeneity: no less than 4 subtypes have been characterized: 5-HT1B and 5-HT1D are labeled respectively with [125I]cyanopindolol, and [3H]5-HT under appropriate conditions. Although some similarities are evident, the pharmacology of the two receptors is clearly different. Rat 5-HT1B receptors recognize with high affinity a number of beta-adrenoceptor antagonists, such as SDZ 21-009, cyanopindolol, pindolol, propranolol and isamoltane. In contrast, calf, pig or human 5-HT1D receptors show significantly lower affinities for these drugs. 5-HT1D receptors show high to intermediate affinities to compounds such as PAPP, DP-5-CT, 8-OH-DPAT, yohimbine and rauwolscine, whereas 5-HT1B receptors have very low affinities for these compounds. The presence of 5-HT1B receptors has been documented convincingly only in rat, mouse and hamster. 5-HT1D receptors have been demonstrated in pigeon, guinea-pig, cat, dog, pig, calf, monkey, and man. The distribution of 5-HT1B and 5-HT1D receptors in all species examined so far, is very similar: high concentrations of sites are found in the nigro-striatal pathway, caudate-putamen, globus pallidus and especially substantia nigra. The subicullum shows also high densities of sites. Similar functional correlates have been proposed to 5-HT1B and 5-HT1D sites. Thus, 5-HT1D receptors are negatively coupled to adenylate cyclase in guinea-pig and calf substantia nigra, and 5-HT1B receptors are negatively coupled to adenylate cyclase in rat substantia nigra. Further, it is established that terminal 5-HT autoreceptors are of the 5-HT1B type in rat cortex, and of the 5-HT1D type in guinea-pig, pig, human and possibly rabbit cortex. In the rat saphenous vein, 5-HT1B receptors mediate inhibition of noradrenaline release. Preliminary evidence suggests that the canine basilar artery and saphenous vein, described as models for "5-HT1-like" receptors, could contain 5-HT1D receptors.(ABSTRACT TRUNCATED AT 400 WORDS)