The effect of fenoldopam on renal haemodynamics and natriuresis in chronic renal failure.

The effect of oral administration of fenoldopam, a dopamine-1 receptor agonist, on blood pressure, renal haemodynamics and natriuresis was studied in 12 patients with chronic renal insufficiency. In addition, the effect of administering a low intravenous dose of fenoldopam on top of the oral dose was compared with the effect of the same intravenous dose given immediately before oral fenoldopam. Oral administration of fenoldopam (50 mg t.i.d. for 3 +/- 1 days followed by 100 mg t.i.d. for 8 +/- 1 days) induced a significant fall in blood pressure (median MAP from 107 to 101 mm Hg). Compared to baseline values, body weight, effective renal plasma flow (ERPF), glomerular filtration rate (GFR) and fractional sodium excretion remained unchanged. Infusion of fenoldopam (0.05-0.1 micrograms/kg/min) on day 1 led to a significant fall in blood pressure (median mean arterial pressure from 107.0 to 98.5 mm Hg), and a significant rise in effective renal plasma flow (median ERPF from 132 to 146 ml/min/1.73 m2). Median fractional sodium excretion increased significantly from 2.1 to 3.3%. GFR, filtration fraction and plasma aldosterone concentration did not change. No relationship was found between the fenoldopam-induced changes in ERPF and natriuresis, nor between baseline GFR or ERPF and fenoldopam-induced urinary sodium loss. Infusion of fenoldopam while patients were on oral fenoldopam had no effect on blood pressure, ERPF or GFR. However, again natriuresis was induced, which did not differ significantly from the fenoldopam-induced natriuresis on day 1. We conclude that oral fenoldopam has a moderate blood pressure lowering effect in patients with chronic renal insufficiency, but exerts no effect on ERPF or GFR. Secondly, a fenoldopam-induced natriuresis does not appear to be related to changes in ERPF or aldosterone secretion.