Renal functional adaptation in the remnant kidney in patients with renal agenesis and in patients nephrectomized in childhood.

The renal response to volume expansion was determined in four patients with renal hypertrophy due to unilateral renal agenesis (URA) and in four patients with renal hypertrophy due to nephrectomy (Nz). Four healthy controls were also studied. The studies were performed during water diuresis and following i.v. infusion of isotonic saline solution. Conventional clearance techniques were used. GFR and PAH clearence were increased to about the same extent in Nz and in URA. Fractional Na+ excretion was highest in the Nz group and lowest in the control group. It was higher in the Nz group than in the URA group. Fractional water excretion (V/GFR) and free water clearance (CH2O) were also determined and the results indicate that the high fractional excretion of Na+ from the hypertrophied kidney can be attributed to reduced fractional reabsorption of filtrated Na+ both in the proximal and the distal tubules. The fractional Na+ reabsorption in the distal tubule appears to be higher in URA than in Nz. It is concluded that glomerular tubular balance for Na+ is more similar to that found in healthy controls if the stimulus to hypertrophy occurs prenatally than if it occurs postnatally.