Binding of yohimbine stereoisomers to α-adrenoceptors in rat liver and human platelets

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Abstract
1 Displacement of tritiated prazosin binding to rat liver plasma membranes and tritiated yohimbine human platelet membranes shows that (+)-yohimbine, alloyohimbine and α-yohimbine (rauwolscine) are selective α2-adrenoceptor antagonists (KDα1/KDα2:635, 46.6 and 112 respectively) whereas corynanthine is more α1-selective (KDα1/KDα2:0.036). 2 11-Methoxy derivatives of α-yohimbine and epi-α-yohimbine are very weak α-adrenoceptor blockers. 3 It is concluded that the aromatic A ring, the Nb atom, and the carboxymethyl moiety are important for the binding of yohimbine to the α-adrenoceptor, the carboxymethyl group being important for the α1/α2 specificity of the molecule.