Systemic and regional hemodynamic effects of acute and prolonged treatment with urapidil or prazosin in normotensive and spontaneously hypertensive rats.

The regional and systemic hemodynamics of urapidil and prazosin were investigated after intravenous (1 mg/kg or 0.01 mg/kg, respectively) and prolonged (three weeks) oral treatment (20 mg/kg a day or 2 mg/kg a day, respectively) in normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats. Following intravenous administration, both urapidil and prazosin decreased mean arterial pressure, mediated through a decrease in total peripheral resistance and accompanied by a transient increase in heart rate in both strains. The changes in regional circulations were more widespread after urapidil, but of longer duration after prazosin. Prolonged administration of urapidil or prazosin resulted in a significant decrease in mean arterial pressure and total peripheral resistance only in SHR. With urapidil treatment, the decrease in vascular resistance was distributed throughout all circulations, with no change in heart rate or cardiac index. Heart rate increased in WKY rats and cardiac index increased in SHR following prazosin treatment. Cardiac mass remained unchanged following treatment with either drug.