Phosphate and the development of nephrocalcinosis in rats fed diets containing alpha protein.

It has been suggested that nephrocalcinosis in rats fed diets containing alkali-treated soy protein may be due to a high availability of phosphate in the diet. In the present study, the development of nephrocalcinosis in rats fed a diet containing 20% alpha protein (an alkali-treated soy protein) was compared with that in rats fed the same diet supplemented with additional phosphate. Phosphate supplementation of the alpha protein diet produced a form of nephrocalcinosis that was morphologically different, at both the light- and electronmicroscopic level, from that obtained with the unsupplemented diet but was quite similar to that obtained with a phosphate-supplemented standard commercial laboratory diet. Levels of serum and urinary calcium and phosphorus and urinary cyclic AMP suggested that a phosphate-induced secondary hyperparathyroidism was present in the rats fed either of the phosphate-supplemented diets, but not in the rats fed the unsupplemented alpha protein diet. The results of this study suggest that nephrocalcinosis in rats fed a diet containing 20% alpha protein, without additional phosphate, is not typically phosphate-induced.