The establishment of an in vivo assay system of bone metabolism using lengthened callus and dual energy X-ray absorptiometry: Age-related decline of bone formation, enhancement by the bone marrow cell transplantation and inhibition of bone formation by bone marrow cell lysate
Medical Journal of Kinki University 19(1): 73-91
The in vivo assay system of bone formation was established using leg-lengthening models in rabbits. The lengthened callus was evaluated quantitatively using dual energy X-ray absorptiometry (DEXA), which was introduced for the first time in the legs of small experimental animals. To obtain a reproducible value correctable for the individual differences in bone mineral density, the percent bone mineral density (% BMD) was introduced. The basal ability in bone formation in the young rabbits was significantly higher than that in the adult rabbits. The callus formation was significantly enhanced by the transplantation of fresh suspended bone marrow cells in both young and adult rabbits, although the enhancement was observed more markedly in the adult rabbits. The enhancement was not detected after transplantation of either freshly separated bone marrow granulocytes of adult rabbits and cultured colony forming cells obtained from young rabbits. The cell lysate of the freshly separated whole bone marrow cells significantly inhibited the bone formation. The cell lysate also reduced the minerals of once formed bone by stimulation of bone marrow cell transplantation. The infusion of culture medium alone did not inhibit the bone formation. These experiments suggest that the inhibition of the bone formation is due to the acceleration of the bone resorption by the release of some cytoplasmic factors.