Comparison of the alpha-adrenoceptor profiles of clonidine and two oxygenated arylamino imidazolines.

The profiles of 2-(3,4-dimethoxyphenylamino)-imidazoline HCl (RX 77171) and 2-[6-(1,4-benzodioxanylamino)]imidazoline maleate (RX 801074) were compared with that of clonidine in isolated tissues and pithed rats. RX 77171 consistently displayed prejunctional alpha 2-adrenoceptor antagonist and postjunctional agonist properties. In contrast, RX 801074 had a complex profile which showed considerable variability between tissues. This variability is highlighted by comparing its effects at the prejunctional alpha 2-adrenoceptors of the isolated vas deferens and guinea-pig ileum; in the former RX 801074 was an agonist whereas only antagonist properties were apparent in the ileum.