Chemical Protection against the Long-Term Effects of a Single Whole-Body Exposure of Mice to Ionizing Radiation: II. Causes of Death

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Abstract
Male BALB/c or C57B1 mice were exposed to different doses of X-rays. Certain groups were given a mixture of protectors or AET [S-(2-aminoethyl)isothiouronium bromide hydrobromide] prior to irradiation; others served as controls. The animals were followed until spontaneous death and the lethal diseases were classified as thymic lymphoma, nonthymic lymphoma, reticulosarcoma, myeloid leukemia, lung carcinoma, liver tumors, sarcoma, glomerulosclerosis, noncancerous lung lesions and others. The data were evaluated by the method of competing risks. Death in nonirradiated BALB/c mice was largely caused by tumors, in particular by lung cancer and nonthymic lymphoma, whereas other causes by tumors, in particular by lung cancer and nonthymic lymphoma, whereas other causes predominate in the C57B1 strain. Radiation-induced life shortening of nonprotected mice was due to increased and advanced incidences of specific diseases, mainly thymic lymphoma in BALB/c mice increases to maximum at 650 R and declined thereafter. A shorter latency period was found for lung carcinoma, although the absolute incidence decreases because of the earlier deaths of the irradiated mice. After AET treatment the maximum incidence of thymic lymphoma in BALB/c mice was shifted to 1000 R but its height was unaltered, whereas treatment with a mixture not only displaced the maximum to a still higher dose but also decreased its frequency. Protection in BALB/c mice was also possible, although to a smaller extent, against myeloid leukemia, sarcoma, glomerulosclerosis and noncancerous lung lesions but it is protection against the 2 latter diseases which contributed most to the prolonged survival in the high dose range. The protection in C57B1 mice resembles that in the BALB/c strain. Thus protection was effective against thymic lymphoma (possibly also against liver adenomas, all carcinomas and myeloid leukemia) and against glomerulosclerosis and noncancerous lung lesions.