Urapidil is an α1 adrenoreceptor antagonist and a 5-HT_1A receptor agonist. IC50 & Target: α1 adrenoreceptor, 5-HT_1A receptor^[1] In Vitro: Urapidil is an α1 adrenoreceptor antagonist and a 5-HT_1A receptor agonist. Urapidil does not affect vascular tone at concentrations up to 10^-5 M. Urapidil (10^-5 M) markedly inhibits the alpha 1-adrenergic agonist (phenylephrine)-induced concentration-dependent contractions in aortic rings without endothelium and also to some extent in those with endothelium. Moreover, the inhibitory effect of Urapidil is more pronounced in rings without endothelium than in those with endothelium. Urapidil (10^-5 M) affects neither the vascular tone nor the concentration-dependent contraction to serotonin^[1].