Receptor binding profile of cyclazosin, a new α1B-adrenoceptor antagonist

Abstract The binding profile of cyclazosin, a new prazosin-related α 1 -adrenoceptor antagonist, at α 1 -, α 2 -adrenoceptors, dopamine D 2 and 5-HT 1A receptors was compared to that of 5-methylurapidil, spiperone, risperidone and other prazosin-related ligands. In addition, cyclazosin was investigated at native and cloned α 1 -adrenoceptor subtypes. Cyclazosin showed high specificity for α 1 -adrenoceptors and a 10–15-fold selectivity for α 1B ( α 1b )-adrenoceptors with respect to the α 1A ( α 1a ) subtype (p K i values of 9.23–9.57 and 8.18–8.41, respectively). However, it failed to discriminate between cloned α 1b and α 1d -adrenoceptors (p K i values of 9.23 and 9.28, respectively).