Action of stereoisomers of (imidazolinyl-2)-2-benzodioxane-1-4 or 2-(2-(1,4-benzodioxanyl))-2-imidazoline (170 150; RX 781094) on peripheral presynaptic and central alpha 2-adrenoceptors.

In the vas deferens of the rat, (-)-170 150 (imidazolinyl-2)-benzodioxane-1-4 or 2-(2-(1,4-benzodioxanyl))-2-imidazoline appeared to be more selective than (+)-170 150 for antagonizing the inhibitory effects of clonidine on the twitch response. In contrast, (+)-170 150 was the most potent of the two isomers for antagonizing the centrally mediated clonidine- or azepexole-induced sleep in chickens. These unexpected results seem to indicate that there are several subpopulations of alpha 2-adrenoceptors.