Seed T M, Kaspar L V, Tolle D V, Fritz T E
Leuk Res. 1987;11(2):171-9. doi: 10.1016/0145-2126(87)90023-3.
Previous studies have shown that continuous whole-body exposure to low daily doses of gamma radiation is highly leukemogenic for beagles initially exposed during either young adulthood or fetal development. In contrast, terminated radiation-exposure regimens (continuous exposure terminated after accumulation of preset total radiation doses) markedly reduce leukemogenic potential. In this study, we examined leukemic incidences and postnatal hematopoietic function in three groups of dogs; continuously irradiated (7.5 cGy/day) during both fetal life and after birth, continuously irradiated during fetal life only, and nonirradiated. Results were compared to results from studies with similarly irradiated and nonirradiated groups of young adult dogs initially tested at 400 days of age. Hematopoietic function was assessed in terms of both circulating blood levels of red cells, platelets, granulocytes, and monocytes, and marrow concentrations and radiosensitivities of hematopoietic progenitors. Results indicated that under continuous 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. These results support the hypothesis, developed from earlier studies with adult dogs, that the processes of acquired radioresistance and recovery in numbers of transformable hematopoietic progenitors are causally linked to early stages of the leukemogenic process under continuous ionizing irradiation.
先前的研究表明，比格犬在成年早期或胎儿发育阶段开始，每天持续全身暴露于低剂量伽马辐射下，极易引发白血病。相比之下，终止辐射暴露方案（在累积预设的总辐射剂量后终止连续暴露）可显著降低致白血病潜力。在本研究中，我们检查了三组犬的白血病发病率和出生后造血功能；在胎儿期和出生后均持续照射（7.5 厘戈瑞/天）、仅在胎儿期持续照射以及未照射。将结果与对最初在 400 日龄时进行测试的、接受类似照射和未照射的成年犬组的研究结果进行了比较。根据红细胞、血小板、粒细胞和单核细胞的循环血液水平以及造血祖细胞的骨髓浓度和放射敏感性来评估造血功能。结果表明，在胎儿期/出生后持续照射的情况下，即高致白血病暴露方案下，出生后造血功能出现明显的、进行性的抑制。这种抑制持续到 100 - 150 日龄，随后是部分造血恢复，这与造血祖细胞获得的放射抗性有关。相比之下，在胎儿期但非出生后持续照射的新生犬，即低致白血病方案，表现出类似的初始造血功能抑制，随后部分恢复。然而，未证明造血祖细胞在时间上相关的放射抗性获得。这些结果支持了从早期对成年犬的研究中得出的假设，即在连续电离辐射下，可转化造血祖细胞数量的获得性放射抗性和恢复过程与白血病发生过程的早期阶段存在因果联系。
