Experimental bone formation induced by decalcified bone matrix is an excellent model in vivo for studying endochondral bone formation. This study investigated the relationship between metabolic status and the onset of initial calcification in a decalcified matrix implanted subcutaneously in rat to characterize changes at discrete phases after implantation.Morphological evaluation and analyses of acid soluble mineral contents revealed that calcification took place on day 12 in regions of hypertrophic cartilage which were newly produced in the bone matrix. Levels of inorganic phosphate ions increased from day 6 and plateaned on day 9. Alkaline phosphatase activities peaked on day 12, and thereafter decreased with the progression of calcification. Energy charge ratio (ECR), which was considered to be an index reflecting the energy status of cells, was found to have shifted to lower values with the onset of calcification. These data support the hypothesis that the metabolic status of cells is closely associated with the beginning of calcification.

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