ObjectivesTo characterize the effects of pressor doses of norepinephrine and low-dose dopamine (3 micro gram/kg/min) on renal hemodynamics in man, as well as to determine the clinical relevance of combining dopamine with norepinephrine.DesignProspective, single-blind, randomized study.SettingCLinical research unit of a tertiary care hospital.SubjectsSix healthy male volunteers ranging in age between 20 and 28 yrs.InterventionsThe subjects were assigned randomly to four treatments (1 wk apart) in which renal hemodynamics and electrolyte excretion were assessed. Treatments consisted of 180-min infusions of the following: a) 0.9% sodium chloride (control); b) pressor doses of norepinephrine; c) dopamine at 3 micro gram/kg/min; and d) pressor doses of norepinephrine and dopamine at 3 micro gram/kg/min. Pressor doses of norepinephrine were defined as doses required to increase mean arterial pressure (MAP) by 20 mm Hg.Measurements and Main ResultsGlomerular filtration rate and renal blood flow were derived from inulin and para-aminohippurate clearances, respectively. Urine output and urine solute excretion were also determined.The mean norepinephrine dose required to increase MAP by 22 plus minus 2 mm Hg was 118 plus minus 30 ng/kg/min (range 76 to 164). After the addition of dopamine, similar doses of norepinephrine resulted in an MAP increase of 15 plus minus 4 mm Hg. Glomerular filtration rate and urine output were comparable under all conditions. The infusion of norepinephrine decreased renal blood flow from 1241 plus minus 208 to 922 plus minus 143 mL/min/1.73 m2(p equals .03). The addition of dopamine returned renal blood flow to baseline values. The clearance of urine sodium increased significantly with the infusion of dopamine alone (p equals .03). All subjects completed the four treatment periods. Adverse events, manifested mostly as palpitations and flushing, were rare and self-limiting.ConclusionsThe addition of dopamine (3 micro gram/kg/min) to pressor doses of norepinephrine normalized renal blood flow in healthy volunteers. These hemodynamic changes were not reflected in urine output and glomerular filtration rate; hence, these monitoring parameters may be unreliable indicators of renal function in the setting of vasopressor therapy. In addition, systemic effects were observed with dopamine (3 micro gram/kg/min), as indicated by a decrease in MAP.(Crit Care Med 1996; 24:1150-1156)