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Experimental ectopic calcification caused by intravenous injection of lead acetate (Pb−Ac) followed by subcutaneous injection of polymyxin B sulfate (PMX) in the rat was studied by the methods of quantitative chemical analysis and X-ray diffraction analysis using samples freed of organic matter by low temperature ashing (LTA). In all specimens, X-ray diffraction data showed the presence of an apatitic phase. In addition, several unknown peaks, the intensities of which weakened with time, were found. These peaks were established to be those of lead pyrophosphate (PbPO) when compared with the Joint Committee on Powder Diffraction Standards (JCPDS), formerly the ASTM index. Improvements in crystallinity of the apatitic phase was accompanied by the increases in the amounts of calcium, phosphorus and carbonate in the LTA ash. The amount of magnesium, on the contrary, decreased from 3 to days. The molar Ca/P ratio was near to 1.5 up to 10 days and then increased to 1.59 at 40 days. When the LTA ash was heated at 600° C, the major crystal phase was β-tricalcium phosphate and the minor phase was hydroxyapatite up to 10 days; after that the relationship between the two phases was reversed. It is suggested that the characteristics of calcium phosphate in the native state was transformed between 10 and 20 days after administration of Pb−Ac and PMX. [ABSTRACT FROM AUTHOR]

The present study is an investigation of the mechanism of hypercalcemia and hyperphosphatemia induced by the intravenous injection of lead acetate (Pb-Ac). A total of 118 male rats were injected with 30 mg/kg of Pb-Ac, or with 16.5 mg/kg of sodium acetate as the control. The levels of serum calcium, phosphorus and lead were then determined at various time periods after the injections. Serum calcium and phosphorus levels increased with time after Pb-Ac injection and the maximum values of calcium (17 mg%) were found after 1 h and of phosphorus (13.5 mg%) after 30 min. Both calcium and phosphorus levels reverted to the normal range after 12 h. The maximum net rates of increase of calcium and phosphorus were found immediately after Pb-Ac injection. At that time, deposition of lead at the calcifying sites of bone and incisor dentin was demonstrated by a histochemical examination. In other experiments the changes in the calcium and phosphorus contents in the medium after shaking bone powder in serum with Pb-Ac in an in vitro system were studied. It was confirmed that the calcium and phosphorus were displaced from the bone mineral, the extent of the displacement being correlated with the concentration of the Pb-Ac added to the medium, and that these displacements were very rapid reactions. These results suggest that hypercalcemia and hyperphosphatemia following Pb-Ac injection results from a direct action of lead on the bone mineral. [ABSTRACT FROM AUTHOR]