Normalization of Mineral Ion Homeostasis by Dietary Means Prevents Hyperparathyroidism, Rickets, and Osteomalacia, But Not Alopecia in Vitamin D Receptor-Ablated Mice1

Abstract

1,25-Dihydroxyvitamin D3 plays a major role in intestinal calcium transport. To determine what phenotypic abnormalities observed in vitamin D receptor (VDR)-ablated mice are secondary to impaired intestinal calcium absorption rather than receptor deficiency, mineral ion levels were normalized by dietary means. VDR-ablated mice and control littermates were fed a diet that has been shown to prevent secondary hyperparathyroidism in vitamin D-deficient rats. This diet normalized growth and random serum ionized calcium levels in the VDR-ablated mice. The correction of ionized calcium levels prevented the development of parathyroid hyperplasia and the increases in PTH messenger RNA synthesis and in serum PTH levels. VDR-ablated animals fed this diet did not develop rickets or osteomalacia. However, alopecia was still observed in the VDR-ablated mice with normal mineral ions, suggesting that the VDR is required for normal hair growth. This study demonstrates that normalization of mineral ion homeostasis can prevent the development of hyperparathyroidism, osteomalacia, and rickets in the absence of the genomic actions of 1,25-dihydroxyvitamin D3.