Increased Tolerance of Mice to Lethal X-Radiation as a Result of Previous Sublethal Exposures.

Abstract

INCREASED RESISTANCE TO RADIATIONutilized for the synthesis of non-essential amino acids by the intact young rat, The possi'bility that urea can !be utilized in anabolic processes in the eviscerate rat should be considered.The possibility that urea can be metabolized in the eviscerate rat weakens one point of evidence that urea synthesis occurs only in the liver. The earlier studies( 1) on nlephrectomized-hepatectomized animals have shown that the blood and tissue urea did not change during the times that these observations were made. The assumption that urea could not be metabolized therefore required the conclusion that no extra-hepatic synthesis of urea could have occurred since the concentration in the body fluids remained uwhanged. However, if urea can be metabolized, it is hypothetically possible for extra-hepatic urea synthesis to coexist with an equal or higher rate of urea metabolism without increasing the concentration of urea in the body. -4s an analogy, it was first assumed that gluconeogenesis occurs only in the liver because the blood glucose falls following hepatectomy. I t has now been clearly established that glucose can >be formed in the kidney, but that this extra-hepatic gluconeogenesis is masked by a higher rate of glucose utilization (1 1). Evi-10. Rose? IT. C., Sniitli: L. C., Wormack, &I., and Shme, M., J. Eiol. Cliem., 1949, 7-181, 307.dence has been reported by Graham, Houchin and Turner(l2) Bhat the active mammary gland of thae goat can synthesize urea.Summary. Male rats of the Sprague-Dawley strain were eviscerated at a weight of 250 g and were given intravenous infusions of solutions of glucose, insulin and 0.9% sodium chloride for periods up to 48 hours. Comparisons were made of the total carcass plus urinary urea in 26 control rats taken immediately following evisceration, 24 rats which weree killed 24 hours following evisceration and, 16 rats which were killed 48 hours following evisceration. The average total carcass urea of the 24-hour rats was lower than that of the controls, and the average value for the 48-hour group was still lower. From the statistical standlpoint, it is hi.gihly probable that there was some extra-renal loss of urea following evisceration. These results are indirect evidence for the Occurrence of urea catabolism. The results are in agreement with observations on other species in showing that there is no rise in the urea concentration of thoe 'body in the absence of the liver.

The Adaptive Response and Protection against Heritable Mutations and Fetal Malformation

“…A number of studies have demonstrated adaptive response at the whole-animal level in vertebrates. Some of the documented positive effects of pre-irradiation have included: reduced short-term mortality rates in mice, [1][2][3][4] reduced frequency of chromosome abnormalities in mice 5,6 and humans [7][8][9] , and reduced risk of cancer development in mice. [10][11][12] These studies provide clear evidence for reduction and/or delay of genetic instability and ultimately disease through adaptive response; however, the majority of both in vivo and in vitro studies have focused on somatic markers of DNA damage or cancer.…”

The radiation adaptive response and priming dose influence: the quantification of the Raper–Yonezawa effect and its three-parameter model for postradiation DNA lesions and mutations

“…At that time he irradiated groups of mice using beta radiation and observed a "recovery from the radiation damage" when the conditioning sublethal dose was applied prior to the test lethal dose. Raper's experiments were repeated a few years later and showed the same effect but no detailed explanation was proposed (Cronkite et al 1950). Next, in the late 1950s, the historical Elkind-Sutton experiments were conducted (Elkind and Sutton 1959).…”

“…1, where the difference between the D 1 + D 2 scheme (with time Δt between doses) and the single D 2 one is denoted as delta (δ) parameter, which is the main quantification of the generalized Yonezawa effect. One has to note, however, that the first observation of this effect (without deeper explanation) was conducted by Prof. Raper in 1940s during the Manhattan Project (Raper 1947;Cronkite et al 1950).…”

Efficacité biologique relative des protons de 3 GeV sur le rat et étude de la radio-restauration par rapport aux y du cobalt 60

“…Cronkite et coll. [33] observent un « surrecouvrement », c'est-à-dire une radio-résistance. Plus récem ment, Nachtwey, Ainsworth, Leong [26] observent sur le porc un recouvre ment de 51 % au 3e jour, de 65 % au 7e jour; la radio-résistance apparaît au 20e jour où la DL 50 est de 164 % par rapport à la DL 50 résultant d'une dose unique.…”