2021 Volume 29 Issue 4 Pages 389-400
Our previous study suggested that a high tripolyphosphate diet rather than a high orthophosphate diet is associated with elevated levels of phosphorus (P), calcium (Ca) as well as calcification in the kidney. Various degrees of phosphate polymerization are used as food additives ; however, no studies have been conducted on their effects in rats fed diets containing high P contents. In this study, rats were fed a high-P diet prepared with polyphosphates with various degrees of polymerization, including disodium phosphate, sodium pyrophosphate, sodium tripolyphosphate, and sodium tetrapolyphosphate. Further, their effects on mineral balance and kidney function, along with expression of mineral transporters were evaluated. In animal experiment 1, male Wistar rats (4 weeks old) were divided into five groups and fed a normal P diet (0.3wt%) and a high-P diets (1.2wt%) prepared with polyphosphate with various degrees of polymerization for 3 weeks. The results indicated that calcification of kidney tissue was higher in rats fed sodium pyrophosphate than in rats fed sodium tripolyphosphate, whereas tended to be lower compared with in rats fed sodium tetrapolyphosphate (p＝0.09). In animal experiment 2, rats were divided into two groups and fed a high-P diets (1.2wt%) with equal amounts of sodium, prepared with disodium phosphate and sodium pyrophosphate. The results indicated that calcification of kidney tissue in rats fed sodium pyrophosphate was tended to be higher than in rats fed sodium dihydrogen phosphate (p＝0.06). Moreover, there was a decrease in the final body weight of rats fed sodium pyrophosphate in both the experiments. Therefore, calcification of kidney tissue due to excessive sodium pyrophosphate intake may be affected by the growth through reduced food intake in rats. To summarize, when food is provided ad libitum, the excess intake of sodium pyrophosphate results in high calcification of kidney tissue compared with other polyphosphates and orthophosphates.
