[Comparative study of piperoxan and 2-(2-imidazolinyl)-1, 4-benzodioxane (170 150) on pre- and postsynaptic receptors in the rat].

1. 170 150 (imidazolinyl-2)-2-benzodioxane 1-4), as does piperoxan, competitively antagonizes the hypertension induced by clonidine in the pithed rat. Piperoxan appears slightly less potent than 170 150 in this preparation as shown by the comparison of the apparent pA10 values: 5.3 for piperoxan versus 5.4 for 170 150. 2. The two drugs antagonize the reduction of the electrically-induced tachycardia produced by clonidine. 170 150 appears to be 3-fold more potent than piperoxan in this preparation. 3. These results are compatible with a blockade of alpha 2-pre and postsynaptic adrenoceptors of the rat by piperoxan and 170 150 appears to be 3-fold more potent than piperoxan in this preparation. 3. These results are compatible with a blockade of alpha 2-pre and postsynaptic adrenoceptors of the rat by piperoxan and 170 150 and they are in agreement with our previous results which indicate that compound 170 150 shows a preferential affinity for alpha 2-adrenoceptors.