[en] Letter to the editor. (author)

[en] Brief item

[en] Gas chromatography-mass spectrometry with selected-ion monitoring was used to measure the yields of radiation-induced base products in aqueous solutions of native or heat-denatured DNA irradiated in the dose range 20-100 Gy. These DNA solutions were saturated with nitrous oxide, nitrogen, air or 20% oxygen in nitrous oxide during irradiation. The products measured were as follows: 5,6-dihydrothymine; 5-hydroxy-5,6-dihydrothymine; 5,6-dihydroxy-5,6-dihydrothymine (thymine glycol); 5-hydroxy-5,6-dihydrocytosine; 5,6-dihydroxy-5,6-dihydrocytosine (cytosine glycol); 4,6-diamino-5-formamidopyrimidine; 7,8-dihydro-8-oxoadenine (8-hydroxyadenine); 2,6-diamino-4-hydroxy-5-formamidopyrimidine; and 7,8-dihydro-8-oxoguanine (8-hydroxyguanine). In oxygenated solutions, 5,6-dihydrothymine, 5-hydroxy-5,6-dihydrothymine and 5-hydroxy-5,6-dihydrocytosine were not formed. The yields of all products, other than 5,6-dihydrothymine, were greater in irradiated DNA samples from N₂O-saturated solutions than from N₂-saturated solutions. (author)

[en] The rate of repair of chromatid aberrations in CHO cells progressing to or arrested in G₂ was compared with the rate of repair of damage which gives rise to G₂ arrest. To measure aberration repair rates, exponentially growing CHO cells arrested in G₂ with 1.5, 2.5 or 3.5 Gy of X-rays were released into mitosis by treatment with 5 mM caffeine immediately or 1, 2 or 3 h after irradiation. Aberration frequencies in these cells were then related to the caffeine-free (repair) interval. To measure rate of repair of arrest-causing damage a split-dose procedure was used. Half-times for aberration repair were approximately 1 h for achromatic gaps and 1.5 h for breaks, intrachanges and interchanges. Half-time for arrest damage repair varied with radiation dose. This result suggests that chromatid aberrations are not a primary cause of radiation-induced G₂ arrest. (author)

[en] The initial response to local γ-irradiation of skin was investigated in fibroblasts from cutaneous explants after doses of 4, 8, 12, 16 or 20 Gy. On the day of irradiation, fibroblast outgrowth was inhibited in a dose-dependent manner, but by day 7 post-irradiation, cell restoration occurred especially in explants exposed to 4 or 8 Gy. The dose-dependent inhibition of fibroblast outgrowth correlated with the decrease in cellular metallo-endopeptidase (MET) activity against succinyl trialanine paranitroanilide. However, the secretion of this MEP activity was 10-fold higher in the culture medium after the lowest irradiation dose (4 Gy.). Its inhibition profile was not modified after local irradiation, whatever the dose. In vivo, the cell density of mastocytes, pericytes and endothelial cells decreased after irradiation. Moreover, damaged collagen was observed in the superficial dermis after local irradiation. (author)

[en] The enhancement of oncogenic transformation in the C3H10T1/2 system by protraction of high-LET irradiation is widely reported. That the reported data follow a clear pattern is shown, and a model whose predictions are quantitatively consistent with these trends discussed. The model, developed from that suggested by Rossi and Kellerer (1986) postulates that cells are especially sensitive to radiation during some period of their cycle. A sensitive period of about 1 h is shown to yield predictions consistent with all available data. (author)

[en] In this outline evaluation of some of the radiobiological processes determining dose-rate effects in biologically targeted radiotherapy, it is concluded that large effects due to repair in normal tissues are possible, especially for late-responding tissues, and radiobiological processes in micrometastases may be significantly modified by the size-dependent absorption of disintegration energy. (U.K.)

[en] The manifestation of DNA damage at the nucleoid level was examined in several AT cell lines using an image analysis system to directly visualize and measure the changes in DNA loop size which occur when increasing concentrations of propidium iodide (PI) are used to titrate the DNA supercoiling response (the 'fluorescent halo assay'). This response consists of a relaxation (0.5 - 7.5 μg/ml PI) and rewinding phase (10-50 μg/ml PI), the latter of which is impaired by the presence of DNA strand breaks in irradiated cells. Results may reflect a greater instability of DNA-nuclear matrix attachment points in irradiated AT fibroblasts. The DNA supercoiling response in irradiated transformed AT fibroblasts and AT lymphoblasts did not differ from that observed in unaffected cells of the same type, but all immortalized cell lines (AT and unaffected) had inherently larger DNA loop sizes than diploid fibroblasts and exhibited excess unwinding after irradiation. (author)

[en] The effects of an acute dose of γ-rays (10 Gy) to post-dormant garlic cloves on inner sprout growth and changes in peroxidases and soluble proteins were evaluated up to 100 days of storage in darkness at 19±1⁰C and 42±2% relative humidity. Radiation-induced inhibition of sprout growth became evident after 25 days of treatment and was synchronous with a marked increase in peroxidase activity. Thin-layer isoelectric focusing revealed that radiation induced an increase in the number of anodic peroxidase isoenzymes at 100 days, suggesting modifications in the vascularization process. Neither the soluble protein content nor the protein pattern were affected by irradiation. These results are discussed in terms of a possible mediating effect of peroxidase on radiation-induced sprout inhibition in garlic. (author)

[en] A proctometroscope has been developed to measure the mechanical functioning of the colon in a murine model. A balloon-tipped probe is inserted into the colorectal region of anaesthetized mice and inflated hydraulically, at a constant rate, by a motor-driven syringe. Compliance (ΔV/ΔP) of the colon was measured at various intervals following X-irradiation, a dose-dependent decrease being observed at 24 weeks. This decrease was progressive with time up to 72 weeks postirradiation. Use of this technique provides fully quantitative data on the function of the colon following radiation injury, and provides an alternative to other physiological assays. (author)