LIGHT-MICROSCOPIC AND ELECTRON-MICROSCOPIC EVALUATION OF THE EFFECTS OF 1,25-DIHYDROXYVITAMIN-D3 ON BONE OF THYROPARATHYROIDECTOMIZED RATS

  • 1 January 1979
    • journal article
    • research article
    • Vol. 97  (2) , 247-+
Abstract
1,25-Dihydroxyvitamin D3 (1,25-[OH]2D3) was administered in doses of 1 (65 pmol) or 5 (325 pmol) units daily for 7 days to adult thyroparathyroidectomized rats fed a normal rodent diet. Both dose levels significantly increased serum Ca2+, decreased serum P, and increased urinary Ca and P concentrations. Numbers of osteoblasts were significantly increased in rats given 5 units 1,25-(OH)2D3. Ultrastructurally, these osteoblasts were larger and interpreted to be more active in bone matrix synthesis and mineralization, compared with osteoblasts in control rats. The number of osteoblasts in rats given 1 unit 1,25-(OH)2D3 was not increased, compared with controls, but they were morphologically similar to the osteoblasts in rats given 5 units 1,25-(OH)2D3. A granular electron-dense material, interpreted to be mineral, was present in the pericellular space of osteocytes in rats given 1 and 5 units 1,25-(OH)2D3. The size of osteocytes, organellar development, and contour of osteocytic lacunae were not affected by 1,25-(OH)2D3. The number of osteoclasts was not significantly elevated in 1,25-(OH)2D3-treated rats and their morphology was similar to osteoclasts in controls. In metaphyseal bone 1,25-(OH)2D3 increased the number and synthetic activity of osteoblasts without significantly enhancing osteoclasis or osteocytic osteolysis. This response was independent of parathyroid hormone and calcitonin in rats fed a normal diet.