Adaptation of renal function after unilateral nephrectomy in children with renal tumors.

Following treatment, survivors of unilateral Wilms tumor (WT) develop structural and functional changes in the remnant kidney. A disproportional increase in functional over structural changes results in hyperfiltration, a condition that may lead to renal damage. We studied adaptation of renal function after uninephrectomy in ten WT patients and a child with renal cell carcinoma. Glomerular filtration rate (GFR) (measured by inulin and creatinine clearances), renal plasma flow (RPF) by para-aminohippurate (PAH) clearances and segmental tubular Na+ transport were studied before and following a protein load (renal functional reserve). Nine patients showed a well-adapted kidney function with a GFR of 82.27 (+/- 5.6), an RPF of 429.71 (+/- 65.6) ml/min/1.73 m2 and a filtration fracton (FF) of 20%. Absolute proximal Na+ reabsorption was 65.2 (+/- 9.6) ml/min/1.73 m2, distal tubular delivery was 18.2 (+/- 3.9) ml/min/1.73 m2 and absolute distal Na+ reabsorption was 2146 (+/- 435) microM/min. A peculiar finding was the high baseline creatinine clearances (176.17 ml/min/1.73 m2) related to increased baseline tubular creatinine secretion. Over 120 min following the protein load, GFR increased by 20%, RPF by 6% and FF remained unchanged. Absolute proximal reabsorption increased by 20% and distal reabsorption by 22%. While most changes in renal function induced by a protein load are similar in healthy individuals and uninephrectomized patients, a more predominant contribution to Na+ reabsorption by the proximal tubule was noted. Postload fractional proximal reabsorption remained at 77% while in healthy persons a decrease from 77% to 62% was reported. Two patients showed dysfunctional changes following nephrectomy characterized by an increased GFR (130 ml/min/1.73 m2), increased filtration fraction (29%) and inability to increase glomerular and tubular functions following a protein load (loss of functional reserve). The significance of these abnormalities is not known and requires long-term follow-up to evaluate whether hyperfiltration will lead to renal damage.