Effect of dietary calcium, magnesium, and phosphorus on phosphate urolithiasis in rats.

Female Wistar rats were fed a basal diet containing various concentrations of calcium, phosphorus, and magnesium: calcium and phosphorus at 0.4, 0.5, 0.8, 1.0, 1.5, and 2 per cent and magnesium at 0.2, 0.4, 0.8, and 1 per cent of the diet dry matter. Two types of uroliths developed: magnesium phosphate in the renal pelves, bladders, and/or ureters of rats fed rations containing 1 per cent magnesium with either 1.0 or 0.5 per cent phosphorus and calcium phosphate uroliths in the renal tubules at the corticomedullary junction of rats fed rations containing phosphorus equal to or greater than 0.8 per cent and magnesium equal to or less than 0.8 per cent. The incidence and severity of calcium phosphate uroliths were reduced by increasing the magnesium concentration in the diet from 0.2 to 0.8 per cent and by increasing the calcium-to-phosphorus ratio to greater than 1. Results of this study indicated that the interactions among dietary calcium, magnesium, and phosphorus seemed to affect the incidence, severity, and type of uroliths in rats.