Abstract
Radioligand binding measurements were performed in membranes of sheep caudate nucleus using [ 3H]5-hydroxytryptamine (5-HT). [ 3H]5-HT labeled a population of high affinity binding sites with a K d of 1.9 ± 0.1 nM and a B max of 19.8 ± 2.2 mol/mg tissue. Combined 5-HT 1D/E binding sites were the predominant 5-HT 1 subtype, accounting for 78% of the total population of 5-HT 1, binding sites. 5-Carboxamidotryptamine (5-CT) and sumatriptan yielded inhibition curves which best fitted a two-site model with high affinity values of 0.8 and 10.1 nM, and 1000 and 206 nM for their low affinity components. The proportion of the high affinity 5-CT and sumatriptan binding sites was 79 and 72%. The binding affinity profile of 5-HT 1D binding sites [5-CT > 5-HT > d-LSD > 5-MeOT > sumatriptan > RU 24, 969 > metergoline > tryptamine = rauwolscine = methylsergide > yohimbine = methiothepin > TFMPP = 8-OH-DPAT > 2-methyl-5-HT > mCPP = quipazine = CP 93, 129 > ketanserin > (-)-propranolol = haloperidol = ipsapirone]compares well to that reported for 5-HT 1D receptor sites in human caudate and cortex (correlation coefficient: 0.99 and 0.98). The present results indicate that sheep caudate nucleus is a valid tissue for studying interaction of compounds with 5-HT 1D binding sites in the relative absence of 5-HT 1E binding sites.
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