International journal of radiation biology and related studies in physics, chemistry, and medicine最新文献

A review is presented on modification of radiation-induced effects in dormant plant seeds. Possible sources of discrepancy of data in the earlier literature are analysed. Approaches to the correct experimental study of mechanisms of interaction of environmental factors in the modification of radiobiological reactions are discussed. Progress in the radiation biology of plant seeds, achieved by precise control of experimental conditions, is considered.

Average doses to rat tissues from the ingestion of 2-[14C]thymidine were compared with those from methyl-[3H]thymidine or 6-[3H]thymidine. Among the three precursors, [14C]thymidine gave the highest dose to spleen and small intestine. The doses to other tissues from [14C]thymidine were almost the same or lower as compared with those from [3H]thymidine, irrespective of the 9 times higher beta-ray energy of 14C than that of 3H. In the case of [14C]thymidine, most of the dose was given by radioactivity incorporated into the organic tissue constituents (non-volatile radioactivity). In the case of [3H]thymidine, however, the dose contributions by non-volatile radioactivity were very small and the major contributions were rather from volatile radioactivity (3HHO), formed by degradation of [3H]thymidine. No significant difference in their total doses was found between the two [3H]precursors, but the dose from non-volatile radioactivity alone was 2-3 times higher with methyl-[3H]thymidine than with 6-[3H]thymidine. Estimates of the dose to cell nuclei in various tissues after the ingestion of [3H]thymidine were also made in order to predict more precisely possible radiation hazards.

Nuclear monolayers, prepared by treatment of mammalian cells with non-ionic detergents, showed increased sensitivity to X-ray-induced DNA double-strand breakage (dsb), as compared with intact cells, due to a decrease in the low-dose 'shoulder'. The DNA dsb dose-response shoulder could be restored by irradiating nuclei in the presence of sulphydryl compounds. However, the ineffectiveness of glutathione, when used at near cellular levels, in restoring the shoulder, suggested a possible role for protein sulphydryls in the radiation response of intact cells.

Hepatocytes were cultured as monolayers and multicellular spheroids, respectively. The uptake of both transferrin-bound metals, iron and plutonium, differed significantly between these two culture systems. The uptake into the multicellular spheroids for plutonium was about 30 times greater, and for iron about 4 times greater, than in monolayer-cultured hepatocytes, which is not a consequence of proliferation and/or de-differentiation of the hepatocytes in the multicellular spheroid culture system. A comparison of the iron and plutonium uptake showed that plutonium was delivered to the cells to an 8-fold greater extent than iron if the hepatocytes were cultured as spheroids. Additionally, the binding of plutonium was not inhibited by preincubation of the spheroids with the iron-transferrin complex. Therefore, we propose that there are two different binding sites for iron and plutonium on hepatocyte membranes.

Spin labeling techniques make possible the observation of oxygen diffusion or concentrations in phospholipid membranes. In such a system, cysteamine, depending upon the molecular cysteamine/DPPC ratio and the pH conditions, inhibits oxygen transport, and this result provides an original explanation for cellular hypoxia after cysteamine administration.

The kinetics of repair of sublethal damage in mouse lung was studied after fractionated doses of 137Cs gamma-rays. A wide range of doses per fraction (1.7-12 Gy) was given with interfraction intervals ranging from 0.5 to 24 h. The data were analysed by a direct method of analysis using the incomplete repair model. The half-time of repair (T1/2) was 0.76 h for the pneumonitis phase of damage (up to 8 months) and 0.65 h for the later phase of damage up to 12 months. The rate of repair was dependent on fraction size for both phases of lung damage and was faster after large dose fractions than after small fractions. The T1/2 was 0.6 h (95 per cent c.1. 0.53, 0.69) for doses per fraction greater than 5 Gy and 0.83 h (95 per cent c.1 0.76, 0.92) for doses per fraction of 2 Gy. Repair was nearly complete by 6 h, at least for the pneumonitis phase of damage. To the extent that extrapolation of these data to humans may be valid, these results imply that treatments with multiple fractions per day that involve the lung will not be limited by the necessity for interfraction intervals much longer than 6 h.

Male mice of the B6C3F1 hybrid strain were whole-body irradiated with different doses of 252Cf/60Co. They were killed 35 days later and spermatozoa from cauda epididymides were stained with eosin-Y. The air-dried smears were examined under light microscope for sperm shape abnormalities. There was an increase in the frequency of abnormal sperm in all the treated groups compared to controls. The RBE for the mixed neutron and gamma radiation of 252Cf was 2.6. The RBE for the neutron component was 3.4. The increased frequency of abnormal sperm was associated with a concomitant decrease in testis weight in the irradiated animals.

Degradation of DNA when gamma-irradiated in aqueous solutions containing cysteine can be efficiently enhanced not only with oxygen, but to the same extent also with Cu2+ ions under hypoxic conditions. The result can be explained by 'self-repair' in this system due to recombination of DNA. with RSS.-R intermediates, and repair inhibition by oxygen or copper involving RSS.-R scavenging. It is emphasized that oxygen enhancement in DNA-thiol systems may occur not only by peroxidation, via defect fixation (DNA-O2.) or thiol activation (RS-O2.), but also by the well-established inactivation of RSS.-R by oxygen. There is evidence also from literature data for a correlation between oxygen enhancement and RSS.-R stability, which varies with thiol concentration, pH and thiol structure.

This electron-microscopic-autoradiographic study was undertaken to identify the cell organelles, which bind plutonium in Chinese hamster hepatocytes at different times after injection. Female Chinese hamsters were injected intraperitoneally with 241Pu and sacrificed at time intervals of between 4 days and 35 weeks. The Chinese hamster was chosen as the experimental animal as it is a species in which there is virtually no elimination of plutonium from the liver. From the 4th day onwards beta-tracks were found over globular electron-dense structures, which were randomly distributed in the cytoplasm of the hepatocytes and strongly resembled lipofuscin bodies. Comparison of the results with those from biochemical experiments showed good agreement between the morphological and biochemical observations. At early times after injection 241Pu was also found in the hepatocyte nuclei. All the evidence suggests that in this species plutonium in hepatocytes becomes bound to lipofuscin-accumulating lysosomes, which cannot be excreted.

Chinese hamster ovary cells grown in vitro were treated with bleomycin or irradiated with high doses of 60Co gamma rays (200 and 400 Gy). DNA strand breaks in single cells were analysed by using our newly introduced microelectrophoretic technique. Bleomycin seems to act in a selective manner so that in some cells the DNA is heavily degraded while in others there is only moderate or no measurable damage. In contrast, a uniform response was found after gamma irradiation. To achieve the same magnitude of DNA fragmentation as in the most severely bleomycin-damaged cells, irradiation with more than 200 Gy is required. Some 8000 double-strand breaks per cell are produced by 200 Gy which will convert the molecular weight of the DNA to the range of 10(8)-10(9) dalton, and free migration of DNA fragments occurs during electrophoresis. We include also a detailed study of the DNA migration pattern following doses of 0-100 Gy gamma rays.