The subcellular distribution of 238Pu and 239Pu in primary cultures of rat hepatocytes

The subcellular distribution of 238Pu and 239Pu after incubation of primary cultures of rat hepatocytes with the citrate complex of these metals was studied, and the results were compared with data from in vivo experiments. As in vivo, the lysosomes are the principal organelles in which 238Pu and 239Pu are accumulated. In contrast to in vivo studies, 239Pu is also detectable on the pericellular membranes and in the cell nuclei, where it is predominantly bound to a high-molecular-weight component. The percentage of the total cellular 239Pu which can be recovered in the cell nuclei increased with incubation time from 10% at 1 h to nearly 30% at 5 h. Plutonium-238, an isotope with 270-fold higher specific activity than 239Pu, showed no association with the nuclei. The membrane-bound fraction of 239Pu, as determined using the exogenous chelator diethylenetriaminepentaacetic acid decreased from 30% at shorter incubation times to 15% at longer incubation periods. After incubation with 238Pu the membrane fraction and the cytosolic fraction contained higher concentrations of the radionuclide than after incubation with 239Pu.     

The antibody-producing cell count of rats exposed to polymeric 239Pu

In experiments with Wistar rats a study was made of the content of antibody-forming cells (AFC) in the spleen at remote times (3 to 12 months) after intravenous injection of 239Pu(IV) in doses of 166, 55, and 18 kBq/kg body mass. The doses absorbed in the central and peripheral immunity organs were defined. Pronounced spleen hypoplasia and profound inhibition of humoral immunity were displayed 1 year after the injection of a small amount of the radionuclide. AFC deficiency in animals was amounted to 11-32 per cent throughout the entire period of observation.     

The induction of liver tumors by 239Pu citrate or 239PuO2 particles in the Chinese hamster

The influence of radiation dose distribution on the frequency of 239Pu-induced liver tumors was evaluated in the Chinese hamster. Different concentrations of 239Pu citrate 239PuO2 particles of known sizes were injected intravenously via the jugular vein. About 60% of the injected 239Pu citrate was deposited in the liver and 40% in the bone. The 239Pu citrate was rather uniformly distributed throughout the liver parenchyma. Injected plutonium oxide particles were taken up by the reticuloendothelial system with 90% of the body burden deposited in the liver. The 239PuO2 particles were localized in the Kupffer cells and produced nonuniform dose distributions that were dependent on particle size. There was an activity- and dose-dependent increase in the incidence of total liver parenchymal cell tumors following injection with either plutonium particles or citrate. For animals that received 14.0-, 2.7-, 0.3-, and 0.04-Gy dose to liver from 239Pu citrate the cumulative tumor incidence was 39, 32, 5, and 0%, respectively. Animals that were injected with the 0.24 micron 239PuO2 particles had doses of 42.0, 7.2, and 0.8 Gy to the liver and tumor incidences of 34, 26, and 5%, respectively. Plutonium citrate also produced hemangiosarcomas of the liver and tumors in bone and bone marrow. The latent period for liver tumor appearance in animals exposed to 239Pu citrate or 239PuO2 particles increased as the injected activity decreased. For animals injected with a similar total activity (7.4 Bq/g), the lifetime cumulative liver tumor incidence was similar for animals exposed to either 239Pu citrate (32%) or 239PuO2 (26%). There was little effect of particle size on liver tumor incidence. These data indicate that, in Chinese hamster liver, local radiation dose distribution is less important in altering tumor incidence than injected activity or average dose. However, the more uniform irradiation from 239Pu citrate administration was more effective in cancer production than the nonuniform irradiation from 239PuO2 particles.     

Calculation of specific energies of incorporated239Pu and131I in accordance with the concept of the critical cell

Summary A better understanding of the effects of energy deposited in cells by incorporated isotopes can be expected from an analysis of differential cell doses. With this thought in mind, the distributions of specific energies in tissue were calculated for²³⁹Pu and¹³¹I. A program written in Fortran IV makes use of a matrix of spherical cells and cell nuclei of 10 and 8 µn diameter, respectively. The cells are arranged in close-packed structure. The radioactivity is considered as being compiled to point sources of 1 dps activity. The sources are located in the common centers of cells and nuclei. The calculations yield discrete values of specific energy using the mass of the nuclei for mass of reference. The numbers of cell nuclei receiving given amounts of specific energy are functions of the specific activity of the isotopes in the tissue. The specific activity is varied by changing the number of sources per g of tissue. The program also allows to calculate the numbers of cell nuclei with zero energy deposition. From the 1 dps point sources an average specific energy of 831 rads/h results for plutonium for cell nuclei within the range of the 5.14 MeV-particles. For iodine, the value is 35 mrads/h within the range of the-particles of 188 KeV mean energy. If the volumes irradiated by the sources begin to overlap these values begin to increase accordingly.     

Frequency of structural chromosome aberrations in the hepatocytes of rats exposed to polymeric 239Pu

Intravenous injection of polymeric 239Pu(IV) nitrate (166.5, 55.5 and 18.5 kBq/kg body mass) to Wistar rats was shown to produce biphase changes in the frequency of hepatocyte chromosome aberrations. The increase in the structural damages to chromosomes at later times of observation was a pronounced function of radiation dose. The absence of such a dependence at early times was evidently due to the elimination of damaged liver parenchyma cells.     

The induction by 239Pu of myeloid leukaemia and osteosarcoma in female CBA mice

Plutonium-239 was injected into 12-week-old female CBA/H mice in the range 1.85-18.5 kBq kg-1 either as a single injection or as 16 injections spaced at 3.5 day intervals over eight weeks. There was a highly significant increase in the yield of fully developed osteosarcomas with increased amounts of 239Pu for both modes of injection. Osteosarcomas too small to be diagnosed radiographically were also seen in many bones and small but significant yields of myeloid leukaemia were seen in animals given plutonium. Although more myeloid leukaemia was seen in the mice given plutonium in divided amounts than in those given the plutonium in a single injection it could not be shown that multiple injection significantly affected the yield of either late effect.     

Long-term effects of combined exposure to external 137Cs gamma-radiation and incorporated 239Pu

A study was made of the delayed effects of mixed exposure to 137Cs-gamma-radiation (a single exposure) and 239Pu (a single intravenous injection) in doses approximating optimal blastomogenic ones. The results are calculated per 1 cGy of weighted mean dose within the body with regard for RBE (1 cSv), per cent of osteosarcomas (per 1 cGy in endosteum and periosteum). A conclusion is made of a complete summation of main biological effects per 1 cSv of the dose absorbed.     

The relationship between 59Fe uptake in marrow and 239Pu deposition in bone.

The marrow in the left femur of each of 17 mice was destroyed by X-irradiation and 59Fe and 239Pu uptake into both femurs was measured 1, 3 and 7 days later. Uptake of 59Fe into marrow was depressed in the left femur 1 and 3 days after irradiation but was enhanced in the right unirradiated femur 3 days after the left femur was irradiated. There was no corresponding depression of 239Pu uptake into the left irradiated femur or enhancement into the right unirradiated femur. These results do not support the view that a functioning erythropoietic marrow is necessary for 239Pu to be deposited in bone.     

On the distribution of genotoxic factors in various organs of mice treated with cycasin

The distribution of genotoxic factors in various organs of mice treated orally with methylazoxymethanol-beta-D-glycoside (cycasin) was investigated using the DNA-repair host mediated assay. Indicator of genotoxic activity was a pair of streptomycin dependent Escherichia coli strains differing vastly in DNA repair capacity; uvrB/recA vs. uvr+/rec+. The animal-mediated assays were performed by injecting mixtures of the two strains i.v. and orally into mice, which were subsequently treated with the test chemical and from which the differential survival of the indicator bacteria present in several organs was determined. The same strains and selection procedures were also used for assessing the DNA-damaging activity in vitro. In the animal-mediated assays in which cycasin was applied orally, significant effects were observed at doses of 100 and 500 mg/kg body weight. The organ distribution of genotoxic factors in the host animal was as follows: the highest genotoxic activity was observed in the liver, followed by intestine and stomach; a clear effect was also observed in the kidneys and, to a lower extent, in the blood stream and in the lungs at the highest dose administered (500 mg/kg body weight). Under in vitro conditions a marginal genotoxic effect was observed even in the absence of liver homogenate, indicating that the test compound is possible activated (hydrolysed) by the E. coli cells. Therefore the genotoxic activity of cycasin observed in the gastrointestinal tract was not unexpected, since the substance was applied orally, thereby exposing the indicator bacteria in these organs to high levels of unmetabolised compound, especially in the stomach. In the intestine members of the microbial flora probably contribute to the metabolic activation of the test compound. The occurrence of genotoxic factors remote from the gastrointestinal tract shows that the present compound or active metabolites thereof penetrate through the intestinal barrier. The extraordinarily high genotoxic activity observed in the liver suggests that the compound is additionally activated in this organ. In compliance with previous in vitro findings this second activation step might lead to the formation of the highly reactive aldehydic form of methylazoxymethanol (MAMAL) mediated by dehydrogenases. Comparison with carcinogenicity studies indicates a good correlation between the distribution of genotoxic effects as determined in the present studies and the localisation of tumors in various organs of rodents treated with cycasin.     

The effective and ineffective levels of the joint action of 239Pu and gamma radiation according to the change in the ECG indices of dogs

Effective and ineffective levels of the isolated and combined action of inhaled 239Pu and external gamma radiation on dogs were estimated by some changes in the ECG. Specific share of each factor in the combined effect and the quality coefficient of 239Pu were estimated by two criteria of changes in the ECG. The data were extrapolated to man by the most reliable criterion, that is, the decrease in the ECG voltage indicated by the sum of R I, II, III waves.