Chronic radiation leukemogenesis: postnatal hematopathologic effects resulting from in-utero irradiation

We examined leukemic incidences and postnatal hematopoietic function in three groups of dogs: (i) continuously irradiated during both fetal life and after birth, (ii) continuously irradiated during fetal life only, and (iii) nonirradiated. Hematopoietic function was assessed in terms of both (a) circulating blood levels of red cells, platelets, granulocytes, and monocytes, and (b) marrow concentrations and radiosensitivities of hematopoietic progenitors. Results indicated that under continous fetal/postnatal irradiation, i.e. the high leukemogenic exposure regimen, a marked, progressive suppression in hematopoietic function occurred following birth. This suppression continued to 100-150 days of age and was followed by partial hematopoietic recovery that was associated with an acquired radioresistance by hematopoietic progenitors. In contrast, neonates that had been continuously irradiated during fetal life, but not postnatally, i.e. the low leukemogenic regimen, exhibited a similar initial suppression of hematopoietic function followed by partial recovery. However, no temporally linked acquisition of radioresistance by hematopoietic progenitors was demonstrated. (author)