(Imidazolinyl-2)-2-benzodioxane 1-4 (idazoxan) and its stereoisomers, new alpha 2-antagonists

Since (+/-) idazoxan is well known as alpha 2-antagonist, the present report described some results on the alpha-adrenoceptor blocking properties of the stereoisomers of idazoxan. At peripheral sites, (+) idazoxan revealed to be equipotent for blocking postsynaptic alpha 1- and alpha 2-adrenoceptors of the rat. On the other hand, it revealed to be a full antagonist of the inhibitory effects of clonidine on presynaptic alpha 2-adrenoceptors of rats. However, in vitro investigations have shown (+) idazoxan to be less selective than (-) idazoxan for alpha 2-adrenoceptors. (-) Idazoxan was selective for postsynaptic alpha 2-adrenoceptors and antagonized presynaptic alpha 2-adrenoceptors of the rat. Results obtained in central investigations revealed species differences between chickens and mice. The present results led to the conclusion that (+) idazoxan was equipotent on alpha 1- and alpha 2-adrenoceptors whereas (-) idazoxan was selective for alpha 2-adrenoceptors. On the other hand, they suggested a stereoselectivity of peripheral and central alpha 2-adrenoceptors for alpha-antagonists.