Renal haemodynamic and neurohumoral responses to urapidil in hypertensive man.

In order to evaluate the acute effects of urapidil on renal vascular tone and on pressor systems we performed a randomised placebo-controlled crossover study in 8 patients with uncomplicated essential hypertension. Each subject received, on two separate days one week apart, an intravenous injection of either placebo or urapidil (25 mg, to be increased to 50 mg if blood pressure did not fall within 5 minutes). Before and following this injection we measured blood pressure and heart rate (Dinamap), renal plasma flow (125I-hippuran), renin, angiotensin II, aldosterone, and catecholamines. The results show that urapidil, when compared to placebo, significantly reduced blood pressure, while increasing heart rate, renal blood flow, noradrenaline and adrenaline. Dopamine levels, on the other hand, were suppressed. While renin and angiotensin II were only mildly stimulated, aldosterone levels increased markedly. It is concluded that urapidil, given intravenously, has an immediate blood pressure lowering effect associated with a fall in renal vascular tone and an increase in renal perfusion. As a consequence both the sympathetic system and the renin-angiotensin system are stimulated, although the latter only to a mild degree. The rise in aldosterone may be related to withdrawal of dopaminergic tone.