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Tamm-Horsfall protein (THP) and epidermal growth factor (EGF) are both synthesized by tubular cells in the distal part of the nephron and excreted with the urine. The present study examines the urinary excretion rates of the two peptides in relation to functional tubular markers in patients with chronic nephropathy. Four groups of patients with moderate to severely reduced renal function were studied: glomerulonephritis (n = 10), diabetic nephropathy (n = 11), tubulointerstitial nephropathy (n = 13), and polycystic kidney disease (n = 8). The renal function was evaluated by glomerular filtration rate (GFR) as an indicator for the general renal function, lithium clearance (C(Li)) as an indicator for proximal tubular function, and absolute distal reabsorption of sodium (ADR(Na)) as an indicator for distal tubular function. The excretion rate of EGF was rather closely correlated with GFR, C(Li) and ADR(Na) (Spearman coefficients of variation 0.88, 0.69, and 0.74, respectively). The correlations between the excretion rate of THP and GFR, C(Li) and ADR(Na) were weaker (Spearman coefficients of variation 0.68, 0.42, and 0.44). When the effect of GFR had been accounted for by multiple variance analyses, the excretion rates of the two peptides were still associated with ADR(Na) but not with C(Li). In conclusion, the urinary excretion rates of especially EGF but also those of THP were correlated with renal function and distal tubular reabsorption of sodium in patients with chronic nephropathy.

We report a 35-year-old man with adult polycystic kidney disease (APKD) that developed nephroptic syndrome accompanied by a rapid worsening of renal function. Histologic examination showed marked tubulointerstitial chronic abnormalities and focal glomerulosclerosis (FGS) lesions in 24% of the glomeruli. With captopril, an renal function continued to deteriorate. No other cases of nephrotic-range proteinuria were detected among 65 APKD patients with renal insufficiency. Histologic examination of an other 12 kidneys removed from patients with APKD showed striking interstitial lesions, most of the glomeruli being normal. However, those patients with higher amounts of proteinuria had more glomeruli (14-32%) with FGS lesions.

Various tubular functions were assessed in 10 patients with polycystic kidney disease (PKD). Three relatively unique abnormalities were apparent in many of these patients -- an inability to maximally concentrate urine, a decrease in ability to lower urine pH after acute acid challenge, and an inability to excrete adequate amounts of ammonium during persistent acid challenge. The defects in urinary acidification and ammonium excretion in PKD have not been previously described.