Increased fractional excretion of phosphate and beta 2-microglobulin in unilateral renal disease

Following progressive nephron loss tubular reabsorption in the remaining nephrons will fall to preserve solute and electrolyte excretion. We have examined the fractional excretion (FE) of phosphate, sodium, beta 2-microglobulin (beta 2M) and tubular glucose reabsorption (T glucose) in children with unilateral renal disease to find 1) the threshold for this response and 2) whether intrinsic renal mechanisms can elicit this response. Separate renal function studies were performed using unilateral ureteral compression. Total glomerular filtration rate (GFR) was 93.7 +/- 2.99 ml/1.73(m2)-1 X min-1, and 110.25 +/- 5.40 in control children. GFR in the scarred kidney (SK) was 22.4 +/- 2.46 and in the contralateral kidney (CIK) 67.2 +/- 4.60 ml X 1.73 (m2)-1 X min-1. The kidney area was reduced in proportion to GFR in SK. FE phosphate and beta 2M were significantly higher in SK than in CIK (sign test), but absolute values for FE phosphate and beta 2M were not higher in SK than in control kidneys. FE sodium and T glucose were the same in SK and CIK.

Following moderate unilateral reduction of GFR selective depression of tubular reabsorption can occur without extrarenal impulses.