Chloride and phosphate as impediments to silica urinary calculi in rats fed tetraethylorthosilicate

Rats fed a dextrose-casein type of diet adequate for normal growth and containing 2% of tetraethylorthosilicate (TES) were used to study the effect of NaCl and Na2SO4 drinking waters, and dietary additions of chloride, sulfate and phosphate on formation of silica urinary calculi. In experiment 1, rats fed the basal-TES diet had a 53% incidence of silica urinary calculi. NaCl or Na2SO4 (0.07 N) drinking waters each increased (P less than 0.01) water intake and urine volume, whereas only NaCl reduced (P less than 0.05) the incidence of silica urinary calculi. The incidence of calculi in the rats treated with NaCl and Na2SO4 was 15 and 55%, respectively. The saline waters had similar effects on urine pH, silica, phosphorus, magnesium and calcium, as well as blood plasma magnesium and calcium. Plasma phosphorus tended to be higher (P = 0.08) in the NaCl-treated rats. In experiment 2, 50% of rats fed the basal-TES diet developed silica urinary calculi. Addition of 0.2 eq/kg diet of chloride, sulfate or phosphate as sodium salts (phosphate was an equal molar mixture of mono- and dibasic sodium phosphates) resulted in a reduction in silica urinary calculi (P less than 0.05) by dietary chloride (15% incidence) and phosphate (5% incidence) but not by sulfate (35% incidence). Water intake and urine volumes did not differ, urine calcium was increased (P less than 0.05) by sulfate, and urine phosphorus was increased (P less than 0.05) by phosphate. Blood plasma concentrations of calcium and magnesium did not differ, but plasma phosphorus was higher for animals fed the additional phosphate (P less than 0.1) or chloride (P less than 0.05) in the 2% TES diet.