High Intake of Sodium Chloride for 28 Days Causes No Effect on Serum FGF23 Concentrations in Cats

SIMPLE SUMMARY: Two important functions of the hormone fibroblast growth factor-23 (FGF23) are the regulation of phosphorus homeostasis and sodium retention. Dietary sodium chloride is known to affect FGF23 level and blood pressure in humans and mice. Furthermore, increased serum FGF23 concentrations are associated with chronic kidney disease, which is the most common cause of death in aging cats. It is therefore of interest to investigate the potential influence of high sodium chloride intake on FGF23. In contrast to findings in mice and humans, high sodium chloride supply did not affect serum FGF23 concentrations in cats. Apparent digestibility of phosphorus, on the other hand, was significantly increased by adding sodium chloride to the diet. Therefore, high dietary sodium chloride concentrations may increase the phosphorus burden on the body. This is especially true when phosphate originates from highly available sources, such as inorganic phosphates with high solubility. ABSTRACT: Background: FGF23 is an acknowledged parameter to assess kidney health. As chronic kidney failure is one of the most common diseases in aging cats, dietary influences on renal health warrant investigation. The purpose of this study was therefore to investigate potential correlations between dietary sodium chloride and FGF23. Methods: In a total of two trials, 11 cats were included. In the first trial, the cats were fed a complete and balanced control diet; in the second trial, sodium chloride was added (8 g/kg/DM)). Blood, urinary, feed, and faecal samples were analysed for major minerals. FGF23 and creatinine were measured in blood and urine samples. Results: Serum phosphate and FGF23 were unaffected by high sodium chloride intake, thus showing no correlation between serum FGF23 and sodium concentrations. Apparent phosphorus digestibility was significantly increased, however, by high sodium chloride intake, whereas apparent digestibility of calcium was unaffected. The present study confirms differences in FGF23 and sodium chloride interaction in cats compared with other species. Further research regarding the correlation between sodium chloride and phosphate homeostasis is warranted.