Lack of effect of vitamin D and its metabolites on intestinal phosphate transport in familial hypophosphatemia of mice.

Intestinal calcium and phosphate transport was studied in normal and hypophosphatemic mice fed a variety of dietary regimens with and without vitamin D. Regardless of dietary phosphorus levels, the genetic hypophosphatemic mice had drastically reduced levels of serum inorganic phosphate and intestinal phosphate transport while showing only slightly reduced serum calcium and intestinal calcium transport levels. The inclusion of vitamin D in the diet did not increase the low serum phosphorus levels and low rates of intestinal phosphate transport in the genetic hypophosphatemic mice, while it did increase serum calcium and intestinal calcium transport levels. The administration of 1,25-dihydroxyvitamin D3 to the hypophosphatemic mice stimulated intestinal calcium transport but had no effect on intestinal phosphate transport. In contrast, the 1,25-dihydroxyvitamin D3 stimulated both phosphate and calcium transport in the intestine of normal mice. The results obtained are consistent with the hypothesis that the primary metabolic disturbance in familial hypophosphatemia involves a defect in phosphate transport mechanisms.