Complete differentiation in vivo of implanted cultured adipocyte precursors from adult rats.

The formation of fully differentiated fat cells from adipocyte precursors, implanted into the same adult rats from which they were derived, is described. Precursor strains of rat epididymal adipocyte strains were grown through five subcultures, some in the presence of radioactive thymidine. While still at a relatively undifferentiated stage, the precursors were re-implanted into a superficial intramuscular location. At the time of resection six months later, "fat pads" were observed at the sites of implantation. These pads contained sheets of cells morphologically identical to mature epididymal adipocytes. The fat cells in pads developing from precursors grown in the presence of [3H]thymidine, were radiolabelled. Therefore, they represent fat cells that have differentiated in vivo from the implanted cultured precursors. Implanted skin fibroblasts did not lead to the formation of adipocytes. The finding that cultured adipocyte precursors from adult rats can differentiate fully not only in vitro, but also in adult animals, supports the probable physiological significance of these cells. The precursors probably participate in fat cell turnover, which likely persists throughout adulthood.