Effect of urapidil on rat brain catecholamine synthesis.

The effects of urapidil, a clinically effective antihypertensive drug, on the in-vivo rate of synthesis of rat brain noradrenaline (NA) and dopamine (DA) was determined. A significant dose-dependent increase in dopa concentration by urapidil after dopa decarboxylase inhibition by NSD 1015 was observed in brain stem (3-30 mg kg-1 i.p.) and striatum (10-30 mg kg-1 i.p.), indicating increased NA and DA turnover, respectively, most probably a result of central blockade of brainstem alpha 1-adrenergic and striatal DA receptors. These results indicate that urapidil may possibly exert its central hypotensive action in part by a reduced influence on brain stem NA, thus reducing central sympathetic outflow.