ACTIONS OF 8-HYDROXY-2-(N-DIPROPYLAMINO) TETRALIN (8-OH-DPAT) AT ALPHA-2-ADRENOCEPTORS

1 We have examined the actions of the 5-HT1A-receptor ligand 8-OH-DPAT at alpha-2-adrenoceptor ligand binding sites in human platelet and rat kidney membranes and at functional pre- and postjunctional alpha-2-adrenoceptors in rat atrium and human saphenous vein, respectively. 2 8-OH-DPAT had low affinity for the alpha-2A ligand binding site of human platelet but showed 10 times higher affinity for the alpha-2B ligand binding site of rat kidney (K1 of 6.41, -log M). 3 In functional studies, 8-OH-DPAT had low potency as an antagonist of noradrenaline-induced contractions in human saphenous vein, with a K(B) of 5.40 (-log M). 4 In rat atria preincubated with [H-3]-noradrenaline, 8-OH-DPAT potentiated stimulation-evoked overflow of tritium with an EC30 (concentration producing 30% increase in the stimulation-evoked overflow) of 6.37 (-log M). 5 It is concluded that 8-OH-DPAT shows selectively for the alpha-4B ligand binding site of rat kidney and for the functional prejunctional alpha-2-adrenoceptor of rat atrium, which resembles the alpha-2B ligand binding site.