Changes in bone mineral in experimentally induced rickets in the rat: Electron microprobe and chemical studies

The elemental composition of trabecular bone was compared for: (a) rats made rachitic on a low phosphorus, vitamin D-deficient diet; (b) rats fed the same diet but supplemented with vitamin D; (c) normal rats fed a standard laboratory diet with normal phosphorus and vitamin D levels. Quantitative energy dispersive X-ray microanalysis was performed on mineralized bone matrix at four sites: (1) clusters of mineral crystals in osteoid; (2) bone matrix adjacent to osteoid containing mineralization clusters; (3) peri-lacunar bone matrix; and (4) deep bone matrix distant from osteocytes. Estimations were also made of serum calcium, phosphorus, and 25-hydroxy-vitamin D, and of calcium, phosphorus, and hydroxyproline in whole bone. At bone sites 2, 3, and 4, the mineral content was greater in the normal group than in the other two groups. At each site, the mineral content of the rachitic bone matrix was greater than that from the vitamin D-treated group. A normal pattern of increasing mineral content with distance into the bone from a recently mineralized border was found in the normal and vitamin D-treated groups but was notably absent in the rachitic bones. Microprobe measurements of Ca:P molar ratios in hydroxyapatite standards and in normal rat bone were approximately 1.7. In both rachitic and vitamin D-treated bones, the Ca:P molar ratio was significantly higher than that in normal bones and correlated with serum Ca:P ratios. It is suggested that the increased Ca:P ratios in the rachitic and vitamin D-treated bones may be explained by an increased carbonate deposition.