The adipocyte component of bone marrow in heterotopic bone induced by demineralized incisor grafts

The relative proportion of adipocytes to hematopoietic elements in the marrow of heterotopically induced bone evaluated 4-42 weeks post implantation of demineralized murine incisors was estimated by histological analysis of hematoxylin-eosin stained tissue sections. Using computerized image analysis of microphotographs,the proportion of nuclear cells vs. adipocytes was ascertained. The percentage of adipocytes in marrow increases over time. Such an effect, the replacement of myelopoietic marrow by adipogenic (yellow) marrow and the resorption of induced bone, is observed in human osteoporosis. A decline in the non-adipogenic cell compartments of bone marrow accompanying induced bone begins in the fourth week of induction, gradually progresses until the 26th week, and does not change after that. The luminosity, a parameter used in image analysis and proportional to the number of nuclear cells, was 124 ± 3 in hematopoietic femoral bone marrow, and that of bone marrow of the induced bone was of a similar value (117 ± 8) in the fourth week. An evident decline in luminosity of bone marrow filling the foci of heterotopic bone was observed in samples taken at nine weeks (82 ± 20). This process progressed until the 26th week, reaching a luminosity of 70 ± 21. At the 42nd week, the luminosity remained at the same level (71 ± 27). This indicates that the replacement of hematopoietic bone marrow of heterotopically induced bone by unilocular adipocytes begins relatively early (the fourth week) and is persistent.