THE ACTION OF MAGNESIUM IN REDUCING RENAL CALCIFICATION IN RATS RECEIVING HIGH PHOSPHORUS SUPPLEMENTED DIET

The changes in the concentrations of calcium in kidney and secreted ho rmone were studied in weanling male rats fed diets either high in phos phorus as phosphate or high in both phosphorus and magnesium. In the f irst experiment, the rats were fed formulated diets containing 0.05% m agnesium added as magnesium sulfate and either 0.5% or 1.5% total phos phorus added as K5P3O10. Calcium and phosphorus concentrations in the kidneys of rats fed the high phosphorus diet were significantly elevat ed. In addition urinary excretion of calcium was decreased and that of phosphorus was increased by high phosphorus administration. The high phosphorus diet also produced significant increase in serum PTH withou t increase in urinary cAMP excretion. In the second experiment, the ra ts fed the same formulated diets supplemented with either 0.05% or 0.2 0% magnesium added as magnesium sulfate after 3 weeks of 1.5% total ph osphorus added as K5P3O10 supplementation. Increasing the intake of ma gnesium decreased calcium concentration in kidney although serum PTH w as still elevated. in conclusion, the effect of magnesium to protect a gainst phosphorus-induced nephrocalcinosis was related with renal rece ptivity for PTH action.