Effect of dietary salt restriction on tubular hypertrophy in rats with early‐stage chronic renal failure

Abstract

Because salt restriction minimizes the occurrence of glomerular hypertrophy and tubular damage, we examined the effect of such restriction in rats with chronic renal failure (CRF). Male Sprague-Dawley rats were fed either a low-salt rat chow (65 mg sodium/100 g) or a normal salt diet (390 mg sodium/100 g) and underwent either 4/5 nephrectomy or a sham operation. Thus, there were four study groups (10 rats in each): a low-salt nephrectomy group (L-Nx); a normal diet nephrectomy group (N-Nx); a low-salt sham operation group (L-S); and a normal diet sham operation group (N-S). At the end of 8 weeks, all the rats were killed. Urinary sodium output, urinary protein excretion and blood pressure in L-Nx were significantly decreased in comparison to the values in N-Nx. Body weight, urine volume and glomerular filtration rate were similar between L-Nx and N-Nx. Histologically, the planar area of glomeruli and the smallest diameter of the proximal tubules in L-Nx were significantly reduced in comparison to those in N-Nx: 8.8+/-0.3 x 10(-3) vs 9.7+/-0.3 x 10(-3) mm2 (p < 0.01) and 6.7+/-0.1 x 10(-2) vs 7.4+/-0.1 x 10(-2) mm (p < 0.01). There were no statistically significant differences between L-S and N-S with the exception of urinary sodium output. Salt restriction in nephrectomized rats minimized the occurrence of proximal tubular hypertrophy independently of renal function. This suggests that salt restriction directly delays the occurrence of both tubular hypertrophy and glomerular hypertrophy in the presence of CRF.