The vascular relaxant effects of guanabenz are not mediated by α2-adrenoceptors in rat aortic rings

The present experiments show that the alpha 2-adrenoceptor agonist guanabenz produced a concentration-dependent relaxation in 5-hydroxytryptamine- and noradrenaline-preconstricted rat aortic rings, but not when tone was raised by high potassium in the medium. Similar findings were made for pinacidil. In 5-hydroxytryptamine-preconstricted preparations the relaxant effect of guanabenz was not affected by yohimbine, propranolol or by removal of the endothelium. In noradrenaline-preconstricted rings the relaxant effects of guanabenz and pinacidil were significantly antagonized by tetraethylammonium. The results suggest that guanabenz might act in the muscle tissue by opening potassium channels or antagonism of calcium mobilization from intracellular stores.