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Study on ectopic calcification in bone marrow of rat tibia caused by vinblastine.

Contact microradiographic study and histological study were performed to investigate the sequential changes in the bone marrow after a large dose of vinblastine or colchicine administration. Rats were injected intravenously with various dose of vinblastine or colchicine. The following dynamic histological changes were noted in the bone marrow in the vinblastine 2.0 mumol/kg and colchicine 2.5 mumol/kg-injected groups: Necrosis of the bone marrow cells was observed in the early stage and the necrotic bone marrow cells were replaced by many fibroblast-like cells. After that, the fibroblast-like cells disappeared and the network-like calcified tissue replaced the region where the fibroblast-like cells existed previously. The osteoblasts were lined on the surface of the ectopic calcified tissue and then the osteoblasts were replaced by the typical osteoclasts. In consequence of this dynamic alteration of the cells, the ectopic calcified tissue decreased and the normal bone marrow cells increased in the bone marrow cavity. The ectopic calcification could hardly be observed in the area where the fibroblast-like cells had not appeared. These findings suggested that the markedly proliferated fibroblast-like cells in the marrow cavity after the administration of vinblastine or colchicine may differentiate to osteoblasts and that the osteoclasts may be derived from the bone marrow cells which had already recovered from the toxic effect of the drugs. The mechanism of the dynamic histological changes in the bone marrow remains to be investigated.