RADIOPROTECTIVE ACTION ON BONE-MARROW CFU DURING IMMOBILIZATION OF MICE

Anesthesia and restraint without anesthesia during whole-body X-irradiation decrease the mortality from both the bone marrow and the intestinal syndromes (30- and 5-day mortality). The 2 types of immobilization decrease the radiosensitivity of the hemopoietic stem cells, as shown by an increased survival of hemopoietic stem cells in the marrow of immobilized mice. The hypoxic cell radiosensitizer Ro-07-0582 [1-(2-nitroimidazolyl)-3-methoxyisopropanol] reversed the radioprotective effect during restraint without anesthesia, but not during pentobarbital anesthesia. Hypoxia of the femur bone marrow cannot explain the decreased radiosensitivity of the stem cells during pentobarbital anesthesia. Pentobarbital also inhibited the recruitment of resting femur bone marrow stem cells (GO-phase cells) into cycle following a sublethal dose of X-rays. The relevance of these observations is discussed.