Changes in vitamin D metabolites and bone histology in rats during recovery from rickets.
The relative roles of 25-hydroxyvitamin D (25-OHD), 1,25-dihydroxyvitamin D (1,25-(OH)2D) and 24,25-dihydroxyvitamin D (24,25-(OH)2D) in bone mineralization are largely unknown. Young vitamin D depleted rats were fed increasing amounts of vitamin D and grouped radiologically in accordance with the rat line test. They ranged from severely rachitic to normal. Radiology was correlated with serum levels of 25-OHD, 1,25-(OH)2D, 24,25-(OH)2D, ionized calcium, magnesium, and phosphate, with bone histology, and with the total mineral content of the animals. Serum 1,25-(OH)2D rose in a linear fashion to supranormal values during bone healing and correlated with the radiological degree of rickets. Serum 25-OHD was below detection limit in the most rachitic and low in the radiologically normal rats, whereas 24,25-(OH)2D was low in all groups. These two metabolites showed no correlation with the radiologic, histologic or biochemical parameters. In rachitic rats, 1,25-(OH)2D appears to play a major role in bone healing and possibly exerts a direct effect on bone cells. It cannot be ruled out, however, that the effect is mediated through a rise in serum levels of calcium and phosphorus, although signs of bone healing were seen in the presence of a subnormal calcium X phosphorus product. Initiation of mineralization can take place with unmeasurable 25-OHD, and 24,25-(OH)2D seems to be without importance.
D000818:Animals; D001835:Body Weight; D001842:Bone and Bones / Q000378:metabolism* / Q000473:pathology; D002112:Calcifediol / Q000097:blood; D002117:Calcitriol / Q000097:blood; D002118:Calcium / Q000378:metabolism; D002762:Cholecalciferol / Q000378:metabolism*; D008274:Magnesium / Q000378:metabolism; D009929:Organ Size; D010758:Phosphorus / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D012279:Rickets / Q000378:metabolism* / Q000473:pathology
D002762:Cholecalciferol; D010758:Phosphorus; D002117:Calcitriol; D008274:Magnesium; D002112:Calcifediol; D002118:Calcium