RSH Data & Documents

"Low Level
Radiation Health
Effects: Compiling
the Data"

Revision 2
March 30, 1999

by Radiation, Science, and
Health, Inc.,
Edited by J. Muckerheide

1.3
Animal and Plant
Biology

1.3.1
Mammals

References

Drs. E. Hahn and W. Ward of the Department of Radiation Biology and Biophysics, University of Rochester School of Medicine and Dentistry, report on rats X-irradiated before mating (1967): "A total of 512 virgin female rats... were subjected to whole-body exposures of 50- to 600-r x-rays on the day of metestrus (M) or 1, 2, or 3 days after metestrus (M+l, M+2, M+3). There was no discernible increase in abnormally developed fetuses in irradiated females. Also the incidence of fetal death was extremely low during the latter trimester of pregnancy. In females irradiated on the day of metestrus there was, like ovulations and implantations, a significant increase in the number of living fetuses following 100 to 600 r (Fig. 1)..."

Drs. John ‘Jake. Spalding, Robert Thomas, and G. L. Tietjen, of Los Alamos National Laboratory, document a life span study of mice as a function of dose, dose-rate, and age in LA-9528 (1982) that: "The results of our study are in general agreement with the results of other researchers in human and animal life span irradiation studies. The largest discrepancy occurs in the abundant lengthening of life spans we saw in younger animals at most dose rates, not allowing an extrapolation to zero dose. ..Our data obtained over widely ranging dose exposure-rate, and exposure-age conditons fail to consistently support any mathematical function that may predict radiation-induced life shortening from radiation exposures approaching backgrourid levels. In fact, our data suggest beneficial effects from low dose and low-dose- rate gamma-ray exposure. Radiation-induced hormesis invertebrates appeared in the literature in the early 1900s.4 Low-1evel external irradiation was shown to increase resistance to various infections and to favorably alter physiological function. Luckey’s monograph’ tabulates specific instances and three recent publications (Luckey 1981, Hickey 1981, Hickey et al 1982) discuss low-level ionizing radiation as a stimulating agent. Luckey reports’ the results of Lorenz et al. (1954) in which gamma-dose rates of 0.11, 1.1, and 2.2 R/day resulted in some instances in increased life spans over the controls (mice, guinea pigs, and rabbits)..."

Drs. S. Brown, G. Krise and H. Pace of the Radiation Biology Laboratory, Texas Engineering Experiment Station, Texas A. and M. College, state (1963): "Groups of 10 mature female rats of the Holtzman strain were exposed continuously to g-radiation levels of 0, 2, 5, 10, and 20 r daily after conception. There were no essential differences in litter size, or in number of offspring born, between four successive litters produced while the mothers remained continuously in the g-radiation field. There was no significant variation in the first six litters born at the 0r, 2r, 5r, and 10r daily radiation levels; however, at 20 r daily only one offspring was born in the fifth litter, and none in the sixth. No anomalies were observed at any level of the radiation used in these experiments, except for a slight decrease in average weight of the newborn.
"Offspring from the third litter born to mothers continuously in the radiation chamber were shown to be fertile in those groups which received 0, 2, and 5 r of radiation administered over a 23-hour period daily. The corresponding animals receiving daily doses of 10 and 20 r from the time of conception were sterile when bred together or with known fertile unirradiated males..."

Dr. Leo K. Bustad and his colleagues discuss irradiation of mice (1965): "Hybrid male mice (C57BL) 5 101) were exposed for 8 hours daily from age 6 to 58 weeks to either 0.1 R/hr or 0.2 R/hr of irradiation and then maintained for their normal life span. The average life expectancy for the two subgroups exposed to 0.1 R/hr was 857 and 870 days, compared with 879 and 966 days for their controls, and for the two subgroups exposed to 0.2 R/hr it was 856 and 894 days, compared with 922 and 918 days for their controls. Growth rates were slightly higher for the irradiated mice than for their controls. The incidence of gross abnormalities was higher in the control subgroups than in the irradiated subgroups at 20 months. No significant increase in tumor incidence was observed in the irradiated groups. Although the dose levels used in these experiments resulted in consistent small differences in patterns of longevity and growth between the averages for the irradiated and control mice, the differences in most instances were small relative to normal experimental variation."

Drs. H. B. Newcombe and J.F. McGregor, of the Biology and Health Physics Division, Atomic Energy of Canada Limited, state: (1972): "An observed 'beneficial' effect from low doses of radiation is described. When mature sperm of rainbow trout were exposed to 25 and 50 rad, the ratios of eggs with embryos to eggs without embryos were significantly increased by approximately 35 and 40%, respectively, as compared with the control. With the higher dose of 400 rad to the sperm the effect was unconditionally 'harmful' and the yield of embryos was greatly reduced. It is suggested that the beneficial effect may be due to changes in the protein of the sperm and the harmful effect to changes in the DNA..."

In the Abstract, Ruda VP and Kuzin AM, in "The occurrence of hormesis during gamma-irradiation of developing rat pups" (1991), states: "Development of rat pups was shown to accelerate (body mass made up 121% of control) after gamma-irradiation on day 21 of the postnatal development (2.88 cGy, dose-rate of 0.12 cGy/h). Higher cumulative doses (14.4 and 144 cGy) did not influence the body mass growth, and inhibition was only caused by doses exceeding 150 cGy."

In the Abstract, Cahill, Wright, Godbold, Ward, Laskey, and Tompkins, in "Neoplastic and life-span effects of chronic exposure to tritium. II. Rats exposed in utero" (1975), stated: "rats were continuously exposed to tritiated water (HTO) from conception through birth in doses of 0, 1, 10, 50, and 100 muCi HTO/ml body water. HTO administration was terminated at birth. Calculated cumulative doses during gestation were approximately 0, 6.6, 66, 330, and 660 rads of total body irradiation. ...the two highest doses resulted in sterile offspring. Animals surviving through 30 days postnatally were defined as the study population and observed until their deaths. Intrauterine exposures to doses up to 66 rads had no significant effects on either sex with respect to life-span, overall neoplasia incidence, incidence rate, or onset of mammary fibroadenomas."

In the Abstract, Iwasaki T, Hashimoto N, Endoh D, Imanisi T, Itakura C, and Sato F, from the Faculty of Veterinary Medicine, Hokkaido University, Sapporo, Japan, in "Life span and tumors in the first-generation offspring of the gamma-irradiated male mouse"(1996),state: "C57BL/6 male mice were exposed to 3 Gy 60Co gamma-rays and mated with unirradiated females after 15 days to produce F1 progeny produced following irradiation of the spermatids. After weaning the offsprings were allowed to live their normal life span. The mean litter size of the irradiated group significantly decreased from 7.1 to 4.9 (p < 0.01), but the sex ratio was not altered by the irradiation. No significant differences in the survival curve and mean life-span between the irradiated and control groups were noted. The only radiation effect in tumour incidence was a decrease of histiocytic sarcoma in female offspring of irradiated males. Except for this, there were no significant differences between the irradiated group and the control group in the incidence or age distribution of tumours."

Professor Don Luckey of the Department of Biochemistry, University of Missouri at Columbia, states (1984) that: "Nishio et al, (1967) found that mice watered with 0.1 Ci 137Cs and 0.4 Ci 90Sr/L  through several generations were more resistant than controls to Ehrlich acites tumor transplants. Upton et al (1970) irradiated mice with single and daily doses of 5 Mev neutrons. Accumulated doses of 15-28 rads resulted in mice with the incidence of tumors below control for both sexes receiving the single dose and for females receiving daily exposures. When specific neoplasms were considered in each sex, twice as many groups showed the hormetic response as all other modes. Hormesis was found in thymic lymphoma and nonthymic lymphomas in both sexes receiving chronic irradiation. Hormesis was noted in female mice exposed in either mode when lung and ovary cancers were recorded. Cahill et al (1975) reported a threshold at 7 rads for radiation induced mammary cancer and total cancers following in utero exposure of mice to tritium. Mowissen and Rust (1976) report data with radiation induced reticuloendothelial cancers which fit the hormetic model; the group irradiated with a low dose of neutrons resulted in fewer cancers than were found in the control mice."

Dr. R. Piispanen, of the Institute of Geosciences and Astronomy, University of Oulu, Finland, writes about hormesis (1995): "Evidence supporting the idea of radiation hormesis can be divided into four broad categories: (1) experiments with plants or animals; (2) human occupational comparisons; (3) regional studies; and (4) experiments throwing light on the effect of radiation at the molecular level."
    "The first pieces of experimental evidence supporting the idea of radiation hormesis derive from the early research of Atkinson (1898) and Davey (1919) referred to above. In more recent times, experiments with animals have been conducted by the (US) National Cancer Institute, for instance. Those carried out in the early 1940s, for example, pointed to a rather unexpected relationship: the irradiated animals had a slightly longer mean life span and greater weight gain than their non-irradiated controls (Henry 1961)...

Drs. K.E. van Wyngaarden and E.K.J. Pauwels of the Department. of Diagnostic Radiology and Nuclear Medicine, University Hospital, Leiden, The Netherlands state (1995) that: "In animals and humans low-level radiation presumably leads to an increase in life span. This increased longevity has been attributed to two factors: (1) an initial production of free radicals (which are thought to be involved in aging (Harman 1986)) as a result of low-level radiation leading to a feedback reduction of intracellular free radical levels; (2) the fact that these phenomena resemble caloric intake restriction effects (Totter 1987) (caloric intake restriction has been found to increase life span (Totter 1985)). Low-level radiation is known to produce oxygen radicals, which affect endocrine balance. This is interpreted by the body as an increased food intake, thus lowering appetite and therefore caloric intake, which in turn increases longevity..."

Drs. M. Yonezawa, J. Misonoh and Y. Hosokawa, of both the Research Institute for Advanced Science and Technology, Osaka, and Komae Research Laboratory, discuss radioresistance in mice (1996): "Preirradiation with 0.05 Gy of X-rays 2 months before a second exposure to a mid-lethal dose significantly enhanced the survival rate in both female and male ICR strain mice. The radioresistance was observed between 2-2.5 months after exposure to 0.05 Gy. It did not appear within 1.5 months, and disappeared after 3 months. This radioresistance was induced only by whole-body preirradiation (not by partial irradiation of the head or the trunk). On the other hand, preirradiation with 0.30 Gy as well as 0.50 Gy resulted in radioresistance 2 weeks later, but not 2 months later. The radioresistance was induced by whole-body preirradiation or partial preirradiation of the trunk. No radioresistance was evident after exposure of intermediate preirradiation doses of 0.15 and 0.20 Gy administered before 2 months and 2-5 weeks, respectively..."

Drs. Akira Ootsuyama and Hiroshi Tanooka of the National Cancer Center Research, Tokyo, Japan report (1993) that: ""The total data indicated that repeated beta irradiation resulted in 100% tumor incidences at 1 to 11.8 Gy per exposure. With 2.5 to 11.8 Gy, tumor emergence followed the same time course (saturation effect). An abrupt delay of tumor emergence occurred when the dose was reduced to 1.5 Gy, and with 0.75 Gy tumors began to appear only at the end of the life span of the mice. With 0.5 Gy per exposure employed in the present experiment, no tumor appeared within the life span of the mice..."