URINARY-EXCRETION OF EPIDERMAL GROWTH-FACTOR AND TAMM-HORSFALL PROTEIN IN 3 RAT MODELS WITH INCREASED RENAL EXCRETION OF URINE

Epidermal growth factor (EGF) and Tamm-Horsfall protein (THP) are synt hesized in the kidneys by the distal tubular cells and excreted into u rine. The urinary excretion of these peptides has been suggested as a potential index for distal tubular function. The urinary excretion rat es of EGF and THP were examined in three groups of rats with increased renal excretion of urine: uninephrectomy, non-osmotic polyuria and di abetic osmotic polyuria. Twenty-four hour urine samples were obtained after 7, 14 and 21 days. The urinary volume per kidney was doubled in uninephrectomy when compared to controls. There was a seven-fold incre ase in urinary volume in rats with non-osmotic polyuria and diabetic o smotic polyuria, as compared to controls. Uninephrectomy, non-osmotic polyuria and diabetes all affected the urinary excretion of EGF and TH P differently. The EGF excretion in uninephrectomized rats was 60-80% of that of the controls, whereas THP excretion was unchanged, indicati ng that EGF excretion varied with renal tissue mass. Non-osmotic polyu ria caused a five-fold increase in THP excretion but no change in EGF excretion. THP excretion in the diabetic rats was increased three-fold after 21 days when compared to controls, whereas EGF excretion was de creased when expressed per kidney weight. Immunohistochemistry demonst rated that EGF and THP were colocalized in the thick ascending limbs o f Henle's loops and distal tubules in all five groups of rats. In conc lusion, the EGF excretion appears to follow renal tissue mass and seem s independent of urinary volume, whereas THP excretion is dependent ma inly on urinary volume. This has implications for the use of EGF and/o r THP excretion rates as an indicator for distal tubular function. (C) 1997 Elsevier Science B.V.