ULTRASTRUCTURAL EVALUATION OF EFFECTS OF 1,25-DIHYDROXYVITAMIN-D-3 ON BONE OF THYROPARATHYROIDECTOMIZED RATS FED A LOW-CALCIUM DIET

  • 1 January 1978
    • journal article
    • research article
    • Vol. 92  (2) , 459-472
Abstract
Thyroparathyroidectomized rats fed a low Ca-normal-P diet were administered 1 or 5 units of 1,25-dihydroxyvitamin D3 (1,25-[OH]2D3) or placebo daily for 7 days. 1,25-(OH)2D3 elevated serum and urine Ca and decreased serum P. Rats given 1 unit of 1,25-(OH)2D3 had increased numbers of osteoclasts in metaphyseal trabeculae. Ultrastructurally, osteoclasts, osteoblasts and osteocytes in rats given 1 unit of 1,25-(OH)2D3, were similar to those in rats given placebo. In rats given 5 units of 1,25-(OH)2D3, osteoclasis was markedly increased. Osteoblasts were more numerous and interpreted to be active in matrix production and mineralization. Lamellated electron-dense bodies were observed adjacent to the plasma membranes of less active osteoblasts and were interpreted to be modified matrix. Most osteocytes in rats given 5 units of 1,25-(OH)2D3 were indistinguishable from osteocytes in rats given placebo. The pericellular space of some osteocytes in rats given 5 units of 1,25-(OH)2D3 contained electron-dense granular deposits that were interpreted to be Ca3(PO4)2 1,25-(OH)2D3 was able to significantly elevate serum Ca independent of dietary Ca, parathyroid hormone, and calcitonin primarily by increasing osteoclasis with minimal dependence on osteocytic osteolysis.