The effect of thymosin application upon radiation sickness in mice.

The mechanism of thymosin effect upon radiation sickness was analyzed in mice. Thymosin (fraction 5) applied before and after a whole-body radiation exposure increased the LD 50/30 of treated animals by 250R. In mice exposed to 500R, thymosin treatment resulted in a faster recovery of haemopoiesis and lymphopoiesis, as indicated by higher bone marrow cellularity, higher lymph node, thymus and spleen weights, and greater 59Fe uptake in the spleen and femur and 125IUdR uptake in the spleens, femur and thymus. The results provide an indication that thymus and its humoral factor markedly influence the haemopoietic stem cells in the population surviving the sublethal irradiation of an organism. They further suggest the existence of feed-back mechanisms between the thymus and harmopoiesis.