Cardiovascular and renal hemodynamic effects of intravenous infusions of the selective DA1 agonist, fenoldopam, used alone or in combination with dopamine and dobutamine.

Fenoldopam (0.1 and 0.2 microgram/kg/min i.v.) was administered to pentobarbital-anesthetized dogs alone and combined with dopamine (DA) and dobutamine. Renal blood flow, heart rate, and mean arterial pressure were measured. Both dosages of fenoldopam increased renal blood flow without altering blood pressure, similar to the effects of DA (1 and 2 micrograms/kg/min). Administration of fenoldopam with only DA (1 microgram/kg/min) produced further increase in renal blood flow. After administration of phenoxybenzamine (15 mg/kg i.v.), DA produced significant increments in renal blood flow and reductions in renal vascular resistance when compared with experiments without phenoxybenzamine, suggesting even low dosages of DA exert alpha-adrenoceptor agonist activity. Dobutamine (2 and 4 micrograms/kg/min) increased renal blood flow about 37% of that produced by DA. Fenoldopam added to dobutamine produced similar increments in renal blood flow as DA. Fenoldopam did not affect the increase in cardiac contractile force produced by DA and dobutamine. Thus, fenoldopam alone or in combination with DA had no advantage over 2 and 4 micrograms/kg/min DA to further increase renal blood flow. In contrast, fenoldopam with dobutamine produced greater increments in cardiac contractile force than DA and equivalent increases in renal blood flow as DA.