ObjectivesTo assess the effects of low-dose dopamine on norepinephrine-induced renal and systemic vasoconstriction in normotensive healthy subjects.DesignOn separate days, either a low-dose dopamine (4 [micro sign]g/kg/min) or a placebo (5% glucose) infusion was added in a single, blinded, randomized order to incremental norepinephrine infusions of 40, 80, and 150 ng/kg/min over a 60-min period each.SettingOutpatient clinic of a university-affillated hospital.SubjectsNormotensive healthy volunteers.InterventionsInfusions of norepinephrine and dopamine.Measurements and Main ResultsBlood pressure and heart rate were measured with a semiautomated device, and glomerular filtration rate and effective renal plasma flow were determined with constant infusions of125I-iothalamate and131I-hippurate, respectively. Norepinephrine alone progressively increased mean arterial pressure to pressor levels, whereas this effect was attenuated by the addition of dopamine (p < .05 vs. norepinephrine alone). Glomerular filtration rate increased during lower norepinephrine doses and did not decrease at the highest norepinephrine dose. Addition of dopamine further increased glomerular filtration rate. Effective renal plasma flow decreased with each norepinephrine alone infusion step, but this decrease was completely prevented by concomitant dopamine infusion (p < .01 vs. norepinephrine). Sodium excretion tended to decrease with norepinephrine, but increased two- to three-fold after addition of dopamine (p < .01 vs. norepinephrine alone).ConclusionsIn healthy man, norepinephrine causes a large decrease in renal plasma flow but not in glomerular filtration rate. Concomitant dopamine administration prevents this decrease in renal plasma flow, increases sodium excretion, and also attenuates the norepinephrine-induced systemic blood pressure increase. These findings warrant further clinical evaluation of the effect of concomitant low-dose dopamine and norepinephrine administration in critically ill patients. (Crit Care Med 1998; 26:260-265)