Acute effects of bunazosin on aortic, vertebral, coronary and renal blood flows of anesthetized dogs.

Effects of 4-amino-2-(4-butyrylhexahydro-1H-1,4-diazepin-1-yl)-6,7-dime thoxy-quinazoline (bunazosin, E-643, Detantol) on aortic, vertebral, coronary and renal blood flows were investigated in anesthetized open-chest dogs. Bunazosin 1, 10 and 100 micrograms/kg i.v. dose-dependently decreased aortic blood pressure (AoP) and inhibited the increase in AoP by phenylephrine 5 micrograms/kg i.v. However, the increase in AoP by norepinephrine 0.5 microgram/kg i.v. remained even after bunazosin 100 micrograms/kg i.v. and was almost undetectable after additional administration of yohimbine 1000 micrograms/kg i.v. A hypotension by bunazosin persisted more than 15 min, but dose-dependent increases in heart rate (HR) induced by bunazosin 1, 10 and 100 micrograms/kg i.v. restored within 2 min. Bunazosin 100 micrograms/kg i.v. significantly but transiently increased aortic blood flow and decreased renal blood flow. Vertebral and coronary blood flows were not significantly changed. Left ventricular dP/dt was transiently increased. Calculated total peripheral vascular resistance and coronary vascular resistance were transiently but significantly decreased. No significant changes were observed in both vertebral vascular resistance and renal vascular resistance. The results indicate that bunazosin maintains the blood flows to brain, heart and kidney, and is continuously lowering AoP without significant changes in HR.