Biological effects of single and fractionated irradiations

One group of mice were irradiated with 100R per day for 5 days (group C-1) and a second group of mice received a single dose of 500R (group C-2). Two days after irradiation, the nucleated cells and CFU-S counts in bone marrow of both groups significantly decreased, especially in group C-2. The damage of capacity of bone marrow stroma in group C-1 was less severe than that in group C-2. Eight days after irradiation, the number of splenic colonies in group C-1 was greater than that in group C-2. Both the damage and the recovery of germinal epithelium in group C-1 appeared earlier than those in group C-2. The damage of germinal epithelium in young mice prenatally irradiated with fractionated doses (group C-3) was more severe than that in those prenaally irradiated with a single dose (group C-4)