EFFECT OF 1,25-DIHYDROXYVITAMIN D3ON PHOSPHATE HOMEOSTASIS IN THE X-LINKED HYPOPHOSPHATEMIC (Hyp) MOUSE

Abstract
We studied the effect of 1,25-dihydroxyvitamin D3 (1,25-(0H)2D3) on homeostasis of inorganic phosphate (Pi) in murine hypophosphatemia (Hyp), a homologue of X-linked hypophosphatemia (XLH) in man. Normal mice given 1,25-(OH)2D3 (83 pg/g-d by continuous subcut. infusion × 10 d) had a significant rise in plasma calcium (Ca) (p < 0.001), plasma Pi (p++-stimulated Pi transport in purified renal brush-border membrane vesicles (BBMV). Hyp littermates did not respond to this dose of 1,25-(0H)2D3. At 415 pg/g-d, Hyp mice had increased plasma CaTp +-stimulated Pi transport in BBMV. At this dose, 1,25-(OH)2D3 also stimulated Pi transport by ev rted sacs of Hyp small intestine (p Hyp intestine. We conclude that l,25-(0H)2D3 improves Pi homeostasis in the Hyp phenotype by its effect on intestine; the defect in renal Pi reabsorption remains unchanged.