Salt-deficient diet and early weaning inhibit DNA synthesis in immature rat proximal tubular cells.

A maturational gradient exists between the inner and the outer cortical nephrons in infant rats. This study compares the putative growth-retarding effects of early weaning (EW) and a salt-deficient (SD) diet in proximal tubule (PT) cells in the inner and the outer cortex. The mitotic response was measured as tritiated-thymidine incorporation in PT cells from 18- to 22-day-old rats. Under basal conditions the mitotic index is the same in the inner and the outer cortex. EW retarded body growth, but had no significant effect on the kidney/body weight (KW/BW) ratio. EW caused a significant decrease in DNA synthesis in both the outer and the inner cortical PT cells, but the effect was significantly more pronounced in the outer cortex. The SD rats had significantly lower levels of serum sodium, lower urinary sodium excretion, slightly decreased BW, but no differences in KW/BW ratio or in dry/wet KW. SD caused a decrease in DNA synthesis in the PT cells in the outer cortex, but not in the inner cortex. In conclusion, two manipulations that can retard proliferation of PT cells, i.e. EW and a SD diet, have a more pronounced effect in immature than in mature PT cells.