Peripheral postsynaptic alpha-adrenoceptor blocking properties of some new dihydrobenzofurane and imidazoline derivatives in pithed rats.

: Peripheral postsynaptic alpha-adrenoceptor blocking properties of six new dihydrobenzofurane and imidazoline derivatives have been investigated in pithed rat against the pressor effects of phenylephrine and cirazoline (alpha 1-agonists) and clonidine and azepexole (alpha 2-agonists). Except for (N-methylimidazolinyl-2)-2 dihydro-2,3 benzofurane (II) that acted neither on alpha 1- nor alpha 2-adrenoceptors, all the compounds revealed blocking effects - plus or minor - on both alpha 1- and alpha 2-adrenoceptors. (Imidazolinyl-2)-2-chloro-7 dihydro-2,3-benzofurane (IV) is equipotent in blocking both alpha 1- and alpha 2-adrenoceptors. 7-Methoxy-(imidazolinyl-2)-2 dihydro-2,3-benzofurane (III) and (imidazolinyl-2)-2-fluoro-7-dihydro-2,3-benzofurane (V) block more effectively alpha 1- than alpha 2-adrenoceptors whereas (imidazolinyl-2)-2-benzocyclobutane (VI) is more potent in blocking alpha 2- than alpha 1-adrenoceptors. (Imidazolinyl-2)-2-dihydro-2,3-benzofurane (I) is a preferential alpha 2-adrenoceptor blocking agent. The most effective agents on alpha 2-adrenoceptors are under further pharmacological investigations.