Effects of simultaneous increases in dietary phosphorus and magnesium concentrations on nephrocalcinosis and kidney function in female rats.

The effects of simultaneous increases in dietary phosphorus (P) and magnesium (Mg) concentrations while maintaining a constant P:Mg ratio on nephrocalcinosis and kidney function in female rats was investigated. Female Wistar rats were fed a control diet (3.12 g P, 0.51 g Mg per kg diet) or a diet having either 3 times the control P and Mg concentrations (3-fold diet; 9.25 g P and 1.42 g Mg per kg diet) or 5 times the control concentrations (5-fold diet; 14.97 g P and 2.37 g Mg per kg diet) for 21 d. The three experimental diets all had same P:Mg molar ratios (control diet; 4.81, 3-fold diet; 5.11, 5-fold diet; 4.96). The 3-fold diet had no significant influence on kidney calcium (Ca), Mg or P concentrations. However, kidney Ca, Mg and P concentrations were significantly higher in rats fed the 5-fold diet than in rats fed the control or 3-fold diets. No significant differences in creatinine clearance were observed among the three groups. Urinary albumin and beta 2-microglobulin excretion were higher in rats fed the 5-fold diet than in rats fed the control or 3-fold diets, while the 3-fold diet had no significant influence on the urinary albumin and beta 2-microglobulin excretion. These results suggest that absolute concentrations of dietary P and Mg are important factors with regard to the development of nephrocalcinosis and diminished kidney function.