Survival of Mice under Duration-of-Life Exposure to Gamma Rays: II. Pathologic Effects

Abstract

A series of experimental groups of equal numbers of male and female LAF1 mice were exposed to duration-of-life Co60 [gamma]-irradiation. The following daily dose levels were used 0 r, 12 r, 24 r, 32 r, 43 r, 49 r, and 56 r, plus a large group of nonirradiated controls. Animals were observed until death at which time they were examined for the presence of tumors or degenerative diseases in an attempt to define the cause of death. The 2 lower daily dose levels, 5 and 12 r/day, were far more carcinogenic than doses above this level. Although the incidence of most tumors is increased at 5 and 12 r/day, duration-of-life exposure is less carcinogenic of accumulated dose than are single and terminated exposures. The reduction in overall tumor frequncy at higher levels could be due to the earlier death or in part to a possible "therapeutic" effect as the dose level increases. Incidence and variety of tumors are much higher in the females, owing for the most part to their high lymphoma incidence and to tumors associated with the reproductive system. Lymphoid, pulmonary, and mammary tumors appear earlier in the irradiated mice, whereas hepatomas, ovarian tumors, and the degenerative diseases nephrosclerosis and am-yloidosis are not affected. Amyloid disease is higher among the males and appears to be more prevalent during the mid-life span. Multiple tumors are common in mice at the lower doses, reaching 50% among the 5-r/day females.