Effect of protein intake on lifelong changes in renal function of rats unilaterally nephrectomized at young age

Changes in glomerular filtration rate (GFR) and urinary protein excretion were determined during a lifelong follow-up period in male WAG/Rij rats, unilaterally nephrectomized (NX) just after weaning, and compared with changes in control rats with both kidneys intact (2K). After surgery, the animals were given either a low-protein (LP; 12%), normal-protein (NP; 24%) or high-protein (HP; 36%) diet. The GFR of 2K-rats was highest with the HP diet and lowest with the LP diet. With all three diets, the GFR of 2K rats remained stable for about 2 years. The mean survival time of 2K rats was not affected by the dietary protein intake and amounted to about 120 weeks. Initially, the GFR of NX rats was highest with the HP and lowest with the LP diet. The GFR remained stable for a period of 36 weeks with the HP diet, 48 weeks with the NP diet, and 72 weeks with the LP diet. Subsequently, the GFR fell linearly in the great majority of cases with all three diets. The highest rate of decline was found in NX rats given the HP diet. As a result, from week 72, the GFR of the NX rats on the LP diet was significantly higher than that of NX rats on either the NP or the HP diet. With all three diets the mean survival time of NX rats was less than that of 2K rats on the same diet. The mean survival time of NX rats on the HP diet was also less than that of NX rats on the LP or NP diet. Proteinuria preceded the fall in GFR in NX rats. The proteinuria was most severe in NX rats on the HP diet, but only moderate with the LP diet. We conclude that, in a rat strain not very prone to develop renal lesions, the GFR of a solitary kidney eventually declines. An LP diet postpones but does not prevent the decline.