title: Light- and electron-microscopic evaluation of the effects of 1,25-dihydroxyvitamin D3 on bone of thyroparathyroidectomized rats.
abstract: 1,25-Dihydroxyvitamin D3 (1,25-[OH]2D3) was administered in doses of 1 (65 picomoles) or 5 (325 picomoles) units daily for 7 days to adult thyroparathyroidectomized rats fed a normal rodent diet. Both dose levels significantly increased serum calcium, decreased serum phosphorus, and increased urinary calcium and phosphorus 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 that of osteoclasts in controls. It is concluded that 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.
mesh_terms: D000818:Animals; D001842:Bone and Bones / Q000187:drug effects* / Q000648:ultrastructure; D002118:Calcium / Q000097:blood; D004100:Dihydroxycholecalciferols / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D006887:Hydroxycholecalciferols / Q000494:pharmacology*; D008297:Male; D010006:Osteoblasts / Q000648:ultrastructure; D010010:Osteoclasts / Q000648:ultrastructure; D010280:Parathyroid Glands / Q000502:physiology; D010758:Phosphorus / Q000097:blood; D051381:Rats; D013961:Thyroid Gland / Q000502:physiology; D013965:Thyroidectomy
chemical_list: D004100:Dihydroxycholecalciferols; D006887:Hydroxycholecalciferols; D010758:Phosphorus; D002118:Calcium