Thermal marrow expansion: effect of temperature on bone marrow distribution

The distribution of bone marrow in adult mammals is limited mainly to those bones deeply embedded in the body and subject to the higher core body temperature. Active marrow is much less prevalent in the limbs. In the past this was attributed to the lower temperature of the peripheral bone marrow. We have studied the possibility of stimulating hematopoiesis in the limbs (and tails) by increasing the limb temperature. This has been done by elevating the ambient temperature of mice and by tail implantation techniques. Mice incubated at ambient temperature of 22 degrees C can be "expanded" to have markedly enhanced marrow activity in the limbs by either incubation for seven days or more at 34 degrees C, or by implantation of the bone into core temperature areas (peritoneal implantation). The increase in marrow activity is shown both histologically and by 59Fe uptake techniques. Anemia does not enhance this effect, indicating a local phenomenon. A variety of experiments suggest that temperature per se and not temperature-induced increase in blood flow is involved. The increase in marrow activity is accompanied by a modest local increase in clonogenic marrow stem cells but it cannot be shown for certainty whether the phenomenon of Thermal Marrow Expansion (TME) is due to the local effect of elevated temperature on stem or stromal cells. The erythrocytes produced by TME appear normal by in vivo fragility testing. TME may have clinical usefulness in man if the phenomenon occurs in the same fashion as rodents.