Diet Calcium Carbonate, Phosphorus and Acidifying and Alkalizing Salts as Factors Influencing Silica Urolithiasis in Rats Fed Tetraethylorthosilicate

Abstract

Three experiments were conducted to determine the effects of excess dietary calcium carbonate, phosphorus and urine acidifying and alkalizing salts on silica urolith formation in a model using rats fed dextrose-based diets containing 2% tetraethylorthosilicate (TES). Diets containing 2% TES lowered weight gains to 91–95% of gains made by rats fed non-TES diets. Urine silica concentrations of rats fed TES were generally in the range of 50–60 mg/dl. In experiment 1, rats fed TES with no additional dietary calcium carbonate had a silica urolith incidence of 35%. With additions of 1 and 2% calcium carbonate to the basal-TES diet, respective urolith incidences were 45 and 60% (r = 0.99, P < 0.02). In experiment 2, monobasic sodium phosphate (MP) providing 0.2% additional phosphorus resulted in a mean urine pH of 6.42 and no uroliths. Dibasic sodium phosphate (DP) without and with 0.5% sodium bicarbonate (SB) resulted in respective urine pH values of 6.78 and 7.14 and urolith incidences of 15 and 20% (MP < DP and DP + SB, P < 0.05). However, the uroliths were small averaging less than 1 mg. In experiment 3, substitution of autoclaved egg albumin for casein, the protein source in experiments 1 and 2, resulted in urine pH of 7.45 and a silica urolith incidence of 46%. An equal-molar mixture of MP and DP providing an added 0.2% phosphorus resulted in a urine pH of 7.07 and reduced the urolith incidence to 4%, and 0.75% of dietary ammonium chloride either with or without the added 0.2% phosphorus gave urine acidification and complete protection from uroliths. Dietary diammonium phosphate also resulted in urine acidification and a 12% urolith incidence. The phosphate and chloride salts used in these studies did not (P > 0.05) increase urine volumes. It is concluded that supplemental dietary phosphorus offers partial protection against silica uroliths that is not associated with increases in urine volume and is only partially dependent on urine acidification. Increases in urolith incidence in rats fed calcium carbonate appear to result from an alkalization of urine and a reduction of urine phosphorus concentration.