Protection by superoxide dismutase of white blood cells in X-irradiated mice

In X-irradiated mice the loss of white blood cells increases exponentially with dose. The dose x_o, which reduces the cell number to 1/e, is 115 ± 15, 205 ± 30, 108 ± 5, and 235 ± 18 rad for leucocytes, granulocytes, lymphocytes and platelets, respectively. The x_o value increases with the amount of endogenous superoxide dismutase per cell. Intravenous bovine superoxide dismutase has no effect on the x_o for granulocytes and platelets but increases it to 145 ± 15 and 143 ± 20 rad for leucocytes and lymphocytes, respectively. The exogenous enzyme also shortens the delay in recovery of the white blood cells, particularly after X-ray doses of 550 and 675 rad. The earlier hematological recovery is attributable to the known radioprotective effect of the enzyme on bone marrow stem cells.