The dynamics of proliferation and differentiation of osteogenic cells under supportive unloading

With the use of radioactive marker of DNA synthesis – ³H-thymidine we have studied the dynamics, peculiarities of proliferation and differentiation of osteogenic cells under hind limb unloading of white rats («tail suspension» method at an angle 35°) during 28 days. The ³H-thymidine was administered at a single dose at the end of the experiment, the biosamples were taken from femoral bones in 1, 48, 96 hr. Light and electron-microscopic radioautography with ³H-thymidine (in 1 hour) have shown, that basic fraction of DNA synthesizing cells in the zones of adaptive remodelling of bone tissue is represented by little-differentiated perivascular cells (that include osteogenic cell precursors). A tendency for a decrease of a labelling index in the ³H-thymidine osteogenic cells on metaphyseal bone trabeculae under hind limb unloading has been established. The dynamics of labelled cells during various time intervals after ³H-thymidine injection testifies to a delay in the differentiation precursors in osteoblasts and their transformation to osteocytes in experiment animals. The obtained data have shown that a long-term supportive unloading leads to lowering the intensity of osteogenetic processes in long bones and reducing bone mass.

Keywords: bone tissue, osteogenic cells, hind limb unloading, radioautography, ³H-thymidine