Dietary Magnesium, Calcium, and Vitamin B6 and Experimental Nephropathies in Rats: Calcium Oxalate Calculi, Apatite Nephrocalcinosis

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Abstract
The effects of varying dietary levels of vitamin B6, magnesium and calcium were studied in rats, in terms of the urinary excretion of various metabolites and of the deposition in the urinary tract of calcium oxalate and apatite. Primary renal deposits of oxalate with secondary obstructive sequelae involving the lower urinary tract occurred in vitamin B6-deficient rats, accompanied by increased excretion of oxalic and xanthurenic acids and by a marked decrease in citric acid excretion. The feeding of diets high in magnesium (400 mg per 100 gm) markedly reduced the deposition of oxalate in vitamin B6-deficient rats although they remained hyperoxaluric. The urinary citrate, however, returned to normal levels or above, whereas the excretion of xanthurenic acid was lowered. The efficacy of high concentrations of dietary magnesium in decreasing renal oxalate deposition in vitamin B6 deficiency appeared related to change in the solvent characteristics of the urine. Varying the dietary calcium level from 0.2 to 1.2%, in conjunction with vitamin B6 deficiency, demonstrated a direct correlation between dietary calcium and the extent of oxalate deposition, an effect that became more pronounced when combined with low dietary magnesium. Distinct differences could be observed between two strains of white rats as to relative sensitivity to vitamin B6 deprivation, judged both by weight gain and extent of renal oxalate deposits. Renal deposition of apatite is correlated inversely with the dietary level of magnesium and directly with the level of dietary calcium. At the commonly used magnesium intake of 40 mg per 100 gm, such deposits were seen in minimal amounts in a quarter of the animals. At this magnesium concentration, deficiency of vitamin B6 protected the animals against apatite deposition. The magnesium requirement of weanling white rats, as judged by the occurrence of renal apatite deposits, would appear to be in excess of 40 mg per 100 gm.