Measurement of renal functional reserve of the single kidney in man.

The renal functional reserve capacity (RFRC) and response of the single kidney to a low protein diet (LPD) were investigated. Effective renal plasma flow (ERPF) and glomerular filtration rate (GFR) were measured using a single injection of I125 Hippuran and Cr51 EDTA during a dopamine infusion (3 micrograms/kg/min) and after 2 weeks on a LPD (0.6 g/kg/day). Dopamine increased ERPF but the associated rise in GFR was not significant. There was a significant decrease in both ERPF and GFR on LPD. The change in GFR during dopamine infusion, but not during LPD, correlated inversely with baseline GFR. Dopamine and LPD had no effect on heart rate or blood pressure and LPD did not alter urinary sodium excretion. These results suggest that the single kidney lacks functional reserve capacity and that protein restriction may be useful in preserving long term function.