Acute effect of urapidil on peripheral serotonin metabolism.

In a cross-over study, the effect of 25 mg urapidil infusion (U, Ebrantil 25, Byk-Gulden, FRG) on serotonin (5HT) metabolism and platelet aggregation (PA) was compared with the effect of placebo (P) in 7 patients with essential hypertension. No changes in 5HT and 5-hydroxyindolacetic acid (5HIAA) plasma levels and platelet 5HT content were observed. PA induced ex vivo by ADP decreased significantly. 5HIAA urinary excretion and fractional excretion (FE) increased, while 5HT renal metabolism changed only moderately. No changes in adrenaline and noradrenaline excretion were observed. In in vitro studies, U in therapeutic levels decreased ADP-induced PA and completely inhibited 5HT-induced PA (platelets of healthy volunteers). It is suggested that U has a direct antiaggregatory effect through 5HT2 receptors of platelets.