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Quantitative histologic methods have been devised to measure several processes dealing with formation and mineralization of matrix and bone resorption. In vitamin D-deficient rats, the total osteoblastic matrix formation rate was 20% less and the total osteoclastic bone resorption rate was 80% more than in pair-fed control rats. These changes were found to be primarily because of changes in the rates of matrix formation and of bone resorption per unit area of forming or resorbing surfaces rather than to changes in the areas of these surfaces. The rate of maturation of osteoid and the rate of initial mineralization both were reduced to half of normal in the vitamin D-deficient rats. These variables related to matrix formation and mineralization were significantly correlated with the concentration of calcium but not with the concentration of phosphate in serum. The occurrence of hypocalcemia is interpreted as the consequence, both of reduced calcium absorption and of inadequate resorptive response of bone cells to homeostatic stimuli, such that, although bone resorption was greater than normal, it did not adequately compensate for the reduced intestinal absorption.

In previous work we found that vitamin D-deficient and also calcium-deficient rats developed hypocalcemia and an impairment of bone formation and mineralization. The present study of thyroparathyroidectomized (TPTX) rats was undertaken to determine the effect of hypocalcemia without secondary hyperparathyroidism. TPTX rats fed a normal diet developed hypocalcemia and hyperphosphatemia in association with impairment of osteoblastic bone matrix formation and of mineralization of newly formed matrix. The serum calcium x phosphorus product was not decreased. The decreased formation was largely due to a reduction in matrix apposition indicating decreased synthetic activity of individual ostcoblasts. In contrast to the above results, when TPTX rats were fed a high-calcium diet to prevent hypocalcemia, no impairment of either formation or mineralization was found. From the results of these two experiments, it is reasonably certain that hypocalcemia was responsible for the inhibition of formation and mineralization. Moreover, based on the magnitude of the changes in serum calcium and bone parameters in TPTX rats, hypocalcemia could have accounted for the inhibition of formation and mineralization in calcium-deficient as well as vitamin D-deficient rats. In TPTX rats the mineralization defect was manifested by decreases in both the rate of osteoid maturation (indicating a delayed onset of mineralization) and the rate of mineralization. A strong correlation (r = 0.95, P < 0.001) was observed between these two rates suggesting a tight coupling of these two aspects of mineralization.TPTX rats also had lower bone resorption rates and higher serum phosphorus levels than sham-operated animals when the normal calcium diet was fed but not when the high-calcium diet was fed. Thus the inhibition of bone resorption in TPTX rats was at least partially prevented by correction of hyperphosphatemia. This is consistent with previous work showing an inverse relationship between serum phosphorus and bone resorption. Accordingly, the depression of bone resorption in TPTX rats was probably due to hyperphosphatemia as well as to hypoparathyroidism.

Quantitative morphologic methods were used to measure the effects of feeding a low phosphorus diet to intact and thyroparathyroidectomized rats on several processes of bone mineralization and turnover. In severely hypophosphatemic animals, the matrix formation rate was decreased, the osteoid maturation rate was decreased, which indicated a delay in the onset of mineralization, the initial rate of mineralization was decreased, and the endosteal osteoclastic bone resorption rate was increased. In moderately hypophosphatemic animals, there was a substantial increase in bone resorption but no change in formation or in mineralization. The increase in endosteal bone resorption was due to an increase in the linear rate of bone resorption and particularly to an increase in the length of the endosteal resorbing surface. The magnitude of the increase in bone resorption was similar in thyroparathyroidectomized and intact rats indicating that neither parathyroid hormone nor calcitonin is involved in this change. This, together with the finding that there was a strong negative correlation (r = -0.99) between the per cent endosteal resorbing surface and the serum phosphorus, supports the view that the increased resorption was due to hypophosphatemia. This inverse relationship between endosteal resorbing surface and serum phosphorus appeared to hold for values of serum phosphorus above normal. The resorptive response to hypophosphatemia, as previously shown for the resorptive response to excess endogenous parathyroid hormone, was partially inhibited by vitamin D deficiency. Increased resorption occurred at levels of serum phosphorus where no changes were observed in bone formation, mineralization, or growth, suggesting that this resorptive response functions as a homeostatic mechanism to maintain serum and intracellular phosphorus concentrations.

Presents a study which discussed the clinical data, calcium metabolic studies and histologic examination of bone in a patient with severe progressive bone demineralization with respect to the etiology of the bone disease. Method of the study; Results and discussion; Conclusion.