Studies on conversion of yellow marrow to red marrow by using ectopic bone marrow implants.

Previous work has suggested that an increase in temperature in conjunction with hemopoietic stimuli can convert yellow marrow to red marrow. Ectopic implantation of yellow marrow in rabbits was used to confirm this suggestion and to determine whether sustained stimulation is needed to maintain hemopoiesis. Tibial marrow (temperature 28.5 degrees C) was implanted in the subcutaneous tissue of the abdomen (temperature 33 degrees C). Phenylhydrazine-induced hemolysis was used as a hemopoietic stimulus. Implants of yellow marrow in control animals, not subjected to modulation of hemopoiesis, led to the formation of fatty marrow nodules. These nodules became hemopoietically active when the hemopoietic stimulus was applied to the animals, either concomitantly with implantation or even two months after implantation. The stimulus was required continuously to maintain the hemopoietic activity of the nodules. These findings confirm that increased temperature acts synergistically with hemopoietic stimuli to induce hemopoiesis in yellow marrow. This supports the concept that, while the total volume of hemopoietic tissue is determined by the body's demands, its distribution may be determined by such factors as local temperature.