Distribution of fibroblastic colony-forming cells in rabbit bone marrow and assay of their osteogenic potential by an in vivo diffusion chamber method.

Rabbit bone marrow has been separated into core, intermediate, and endosteal cell populations. When plated out in vitro, each of the fractions gave rise to colonies of fibroblastic cells. The colony-forming efficiency increased from the core population by a factor of 4 to a maximum of 3.4 X 10(-6) in the endosteal fraction. The osteogenic potential of each fraction was determined following their implantation in diffusion chambers into host rabbits. Each of the indices of osteogenesis (alkaline phosphatase activity, Ca and P accumulation) were significantly lower in the core population than in the two populations closer to the bone surface. Our results are consistent with the hypothesis that the osteogenic precursor cells of marrow belong to the fibroblast colony-forming cell fraction, and indicate that these cells, although found throughout the marrow, are concentrated close to the bone surface.