Efaroxan (RX 821037) is a potent and selective ?(2)-adrenoceptor antagonist in human frontal cortex membranes.
The antagonist [(3)H]idazoxan binds with comparable affinity to ?(2) adrenergic receptors and to non-adrenergic "idazoxan sites" in human frontal cortex membranes (K(D) = 23 and 28 nM). RX 811033, the 2-ethyl derivative of idazoxan, displays about equal affinity for the ?(2) receptors as idazoxan but much lower affinity for the idazoxan sites (K(i) = 19 nM and 28 ?M). Compared to RX 811033, efaroxan (RX 821037) has a dihydrobenzylfuranyl ring system instead of a benzodioxan ring. Nevertheless, efaroxan and RX 811033 bind with equal high affinity to the ?(2) receptors and with equal low affinity to the idazoxan sites. Radioligand binding studies with [(3)H]RX 821002, the 2-methoxy derivative of [(3)H]idazoxan, confirm that efaroxan is an ?(2) adrenergic antagonist possessing high affinity for the ?(2) receptors and high ?(2) receptor/idazoxan site-selectivity in the human frontal cortex.
de Vos
H
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Department of Protein Chemistry, Free University Brussels (V.U.B.), 65 Paardenstraat, 1640 St Genesius-Rode, Belgium.
de Backer
J P
JP
Vauquelin
G
G