Fractionated irradiation and haematopoiesis. II. The effect of bone-marrow cell transplants in conditions of split dose of irradiation.

Haemoregeneration after the irradiation with 600 R was studied using two different fractions given before and after the transplantation of bone-marrow cells. The dose of 600 R was divided in two uneven fractions: 500 + 100 R, 400 + 200 R and 300 + 300 R. During the free interval between the two doses (5 min) transplantation of bone-marrow cells was performed. Recolonization of bone-marrow and spleen was analysed on the 10th day after treatment. For analysis, samples of blood, bone-marrow and spleen were used. Maximal effect was found in the experimental group of animals irradiated with 500 R before and with 100 R after marrow-cell transplantation. Minimal haematopoietic response was in the group irradiated with 300 R before and after transplantation. This points at the importance of the primary dose for acceptance of the transplants and their activation.