Selective renal dopamine-1 receptor stimulation in man.

The selective dopamine-1 (DA-1) receptor agonist, fenoldopam, was studied during intravenous administration to ten normal male subjects on a diet of 150 mEq sodium and 60 mEq potassium per day to determine the mechanism of dopamine-induced natriuresis. During DA-1 receptor stimulation, urine flow rate and renal plasma flow manifested a biphasic increase. Urine flow rate increased from a control of 13 +/- 1 to 17 +/- 1.2 ml/min and again to a peak of 16 +/- 1. Renal plasma flow increased from 344 +/- 39 to 481 +/- 44 ml/min and then to 497 +/- 38. Sodium excretion (UNaV) and fractional sodium excretion (FENa) demonstrated a sustained increase. UNaV rose from a control of 0.21 +/- 0.03 to 0.32 +/- 0.05 mEq/min. FENa rose from a control of 1.6 +/- 0.1 to 2.7 +/- 0.6%. Fenoldopam did not alter glomerular filtration rate. The association of changes in renal plasma flow and in UNaV and FENa demonstrate in man that DA-1 receptor stimulation causes natriuresis by direct renal tubular action. The renal tubular effect appears to be a major determinant of the degree of natriuresis.