Lack of Effect of Vitamin D and Its Metabolites on Intestinal Phosphate Transport in Familial Hypophosphatemia of Mice1

Abstract

Intestinal Ca and P transport was studied in normal and hypophosphatemic mice fed a variety of dietary regimens with and without vitamin D. Regardless of dietary P levels, the genetic hypophosphatemic mice had drastically reduced levels of serum Pi and intestinal P transport while showing only slightly reduced serum Ca and intestinal Ca transport levels. Inclusion of vitamin D in the diet did not increase low serum P levels and low rates of intestinal P transport in genetic hypophosphatemic mice, while it did increase serum Ca and intestinal Ca transport levels. Administration of 1,25-dihydroxyvitamin D3 to hypophosphatemic mice stimulated intestinal Ca transport but had no effect on intestinal P transport. The 1,25-dihydroxyvitamin D3 stimulated P and Ca transport in the intestine of normal mice. The primary metabolic disturbance in familial hypophosphatemia apparently involves a defect in P transport mechanisms.