Effect of Bone Marrow-Spleen Injection After Fast Neutron Irradiation in Mice

¹ From the Biological and Medical Sciences Division, U. S. Naval Radiological Defense Laboratory, San Francisco, California

Following exposure to midlethal and supralethal doses of 2 mev and 8 mev neutrons from the cyclotron, a single intravenous injection of fresh isologous bone marrow suspension containing 1 x 10⁶ nucleated cells, or a single intraperitoneal injection of isologous infant spleen homogenate was given. At neutron doses (550–700 rep) which elicited 100% mortality by 8 days in the controls, injection of bone marrow had no beneficial effect on survival. Following neutron doses in the midlethal range (380–400 rep), bone marrow injection elicited a slight increase (relative to buffer-injected controls) in the percentage of mice surviving at 8 days—57% versus 35%. During the 9–14-day period, a smaller proportion of mice (as a percentage of 8-day survivors) died in the bone marrow-treated group, compared with the controls—18% versus 60%, respectively. The over-all 30-day survival was 23% for the marrow-treated mice, and 14% for the controls. At this dose level, furthermore, deaths occurred during the 3rd and 4th weeks postirradiation in the face of apparently adequate bone marrow regeneration, as judged histologically, and the time distribution of deaths was essentially the same whether marrow was administered or not. These data, in sharp contrast with those observed following lethal doses of x-rays in mice, imply that the deaths following 2 mev neutrons in the midlethal range involve a mechanism different from that of x-rays at comparable doses—possibly the consequences of a delayed or secondary intestinal injury.