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 degrees) 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.