Pharmacological activities of the antihypertensive drug urapidil in the rat.

Urapidil had blocking activity on alpha 1-adrenoceptors in the rat isolated caudal artery (pA2 congruent to 7) and in the anaesthetized rat. Urapidil had no clonidine like agonistic activity on alpha 2-adrenoceptors in preparations of the guinea-pig ileum (prejunctional) or dog saphenous vein (post-junctional). Urapidil (0.01-0.1 mg/kg i.v.) had a hypotensive effect in the anaesthetized rat. In a dose of 0.1 mg/kg, the depressor response was accompanied by bradycardia. Vagotomy abolished the bradycardia and attenuated the depressor response. The results indicate that the antihypertensive effect of urapidil may be due partly to blockade of postjunctional alpha 1-adrenoceptors, but in addition there is a central component of action.