Different Doses Of X-rays Research Articles

Induction of lung tumours by the action of radiation and urethane.

IN a recent paper, Foley and Cole1 reported some investigations of the incidence of lung tumours in mice exposed to different doses of X-rays, followed by an injection of urethane. They assumed that the lung tumours are induced by the urethane and that the X-rays have an inhibitory effect on the tumour incidence. On this basis they interpreted their results as showing a dependence of this inhibitory action on radiation dose with a threshold of about 300 rads.

Radiosensitivity in Plants : I. Relation between the water content of some crop seeds and their sensitivity to different doses of X-rays and γ-rays

1. Relationship between the water content of dormant seeds of several plants and their sensitivity to X-rays and γ-rays was studied. 2. Sensitivity of dormant seeds to various radiations was at a minimum when they contained from about 12 to 18% water, except for rape seeds. 3. Resistance of dormant rape seeds to T-rays was at a maximum when they contained from 5 to 8 % water. 4. In general, sensitivity of dormant seeds of various plants to radiation is increased by either a low or a high water content.

STUDIES ON THE RADIOSENSITIVITY OF MONONUCLEAR INFLAMMATORY CELLS, IN VITRO.

SummaryMononuclear cells were irradiated in vitro with different doses of x-rays. RNA-labelling with 32P was studied. After irradiation (5000–10 000 r) there was a decrease of specific activity in the total RNA as compared with the control cells. This initial effect of x-rays on RNA-labelling proved to be reversible after a few hours (2–3) after irradiation. The RNA specific activity of irradiated cells was studied in the phenol-released fraction, in that remaining in the phenol phase and in the different fractions of RNA separated on ECTEOLA. The initial decrease of specific activity was demonstrated in all fractions. Under such circumstances the immediate effect of x-ray on RNA-labelling is questionable.

Changes in metabolic activities of hepatoma cells following increasing x-ray doses.

IT has been reported that aerobic and anaerobic glycolysis in the Yoshida ascites sarcoma are markedly impaired following in vitro irradiation with a dose of 20 kr. of X-rays. In these conditions uptake of oxygen is slightly decreased1. A lowered incorporation of alanine labelled with carbon-14 into protein of the ascites-sarcoma, cells was also noted under anaerobic conditions2. More recently the in vitro irradiation of Ehrlich ascites tumour cells with different doses of X-rays (20–300 kr.), was found to stimulate both oxygen consumption and aerobic glycolysis whereas anaerobic glycolysis decreased as the X-ray dose increased up to about 200 kr. (ref. 3).

The Radiosensitivity of the Processes of DNA-synthesis in Mouse Spleen

SummaryThe effect of different doses of x-rays on DNA-synthesis in mouse-spleen lymphocytes during the synthetic period has been studied in vivo and in vitro. DNA-synthesis was measured by the incorporation of 3H- or 14C-thymidine. The data have confirmed that the radiosensitivity is markedly greater in vivo. The discrepancy was not readily remedied by fortification of the incubation medium by ‘energy-producing’ substances, and the increased depression does not seem to be due to the release of DNA-metabolites or an inhibitor of DNA-synthesis by the intact spleen. A triphasic response for lymphocytes in vivo is postulated to explain the greater radiosensitivity.

Effect of Ultraviolet Pretreatment on Yield of Mutations by X-rays in Wheat

A decrease in the yield of chromosomal aberrations in root meristems of wheat induced by four different doses of x-rays has been found to occur when the seeds are pretreated with ultraviolet radiation. However, in X(2) generation, the mutation rate for combined treatment is lower than for x-rays alone in lower dosages and higher than for x-rays alone in higher dosages.

Vaccinal tularemic infection in guinea pigs affected by radiation sickness

Different doses of x-rays (from sublethal to 50–70 LD)administered 24 hours before the vaccination or 24 hours after it do not cause exacerbation of the vaccinal tularemic infection in guinea pigs immunized with live microbes of vaccinalB. tularense strain. As shown, no reversion of the vaccinalB. tularense strain is possible in these conditions. In our experiments irradiation had a more pronounced effect on the allergic reconstruction of the body than on the formation of the antibodies, and this is probably due to a more pronounced radiosensitivity of the mechanisms effecting the process of allergization of the body as compared to those of antibody formation.

A quantitative study of the sensitivity of oocytes to x-irradiation.

In a quantitative study of the reaction of the rat ovary to X-irradiation, a curvilinear relationship has been established between the number of oocytes that survives exposure to X -rays, and (i) the dose of irradiation, and (ii) the time after exposure. The speed with which an individual oocyte disappears seems to be largely independent of the dose of X -rays. The population of oocytes decreases very rapidly during the first 18 h after X-irradiation, the rate of decline after 24 h being almost negligible. Primordial oocytes are more radio-sensitive than those in later stages of development. The lowest dose of X -rays which destroys most of the primordial oocytes within 18 h is about 300 r. With the possible exception of Graafian follicles, follicles in later stages of development require much higher doses of irradiation before degenerating. The tolerance of ‘medium-sized' follicles would thus appear to be responsible for the fact that the dose which is necessary to sterilize adult rats is extremely high (4400 r). The results also show that the proportion of oocytes destroyed by a given dose of X -rays depends partly on the age of the animal at the time of exposure. The younger the animal, the higher the proportion of oocytes which are eliminated. Multiple regressions have been calculated according to the formula y = a + b 1 x 1 + b 2 x 2 + b 3 x 3 , where y = log 10 count of oocytes x 10 2 , x 1 = log 10 age in days x 10 2 , x 2 = log 10 dose of X -rays in r x 10 2 and x 3 = log 10 post-operative period in h x 10 2 . It is thus possible, by means of regression coefficients a , b 1 , b 2 and b 3 , to obtain an estimate of the numbers of oocytes in different stages of development which are likely to survive after the ovaries have been exposed to different doses of X-rays.

Effect of x-radiation on pollen tube growth and seed setting in crosses between Nicotiana tabacum and N. rustica.

In vitro andin vivo studies of the effect of irradiating pollen with different doses of X-rays were carried out inNicotiana rustica andN. tabacum. Dosages upto 9600 r were found to enhance the rate of growth of pollen tubers per unit time. Advantage was taken of this observation to overcome the incompatibility normally found in the crossN. tabacum x N. rustica as a result of the inadequate growth ofrustica pollen tubes intabacum style. Thus, whenrustica pollen exposed to 4800 r and 9600 r of X-rays were used to pollinatetabacum, fertilization resulting in the formation of viable hybrid seeds occurred. In the crossN. rustica×N. tabacum there is partial seed failure as a result of the hyperplastic development of the nucellar and endothelial cells. However, when X-rayedtabacum pollen were used in the cross, seed development registered a marked improvement. Since there is now evidence for suggesting that the contents of even those pollen tubes which do not participate in fertilization have some role to play in the development of the seed, it seems likely that radiation-induced biochemical changes in pollen may prove advantageous when conditions for seed development are abnormal as in instances of somatoplastic sterility. Besides such indirect biochemical effects, irradiation of pollen may also lead to genetic changes resulting in the inactivation of zygotic lethals. Thus, there is much scope for investigating the use of radiation to overcome inter-specific and inter-generic cross-incompatibility barriers.