Current topics in radiation research quarterly最新文献

Multicell spheroids provide an in vitro tumour model of intermediate complexity between tumours and standard cell cultures. Spheroids of several varieties of normal and tumour cells have been grown and Chinese hamster V79-171b cells have been studied in detail. Spheroids simulate conditions in those solid tumours which contain nodular areas with necrosis at a distance from blood vessels and show a decrease in growth fraction as they increase in size. They contain radiation resistant chronically hypoxic cells which develop spontaneously as the spheroids grow, and exist in a tumour-like environment, yet retain their growth potential. Several assays have been developed or adapted for use in spheroid experiments to study cell properties and responses to treatment. These include many of the techniques used in tumour biology to determine the net response of the tumour, such as volume changes, histology, and net cell survival as well as more direct assays involving separation of subpopulations of cells. Methods were also developed to study in situ repair and repopulation processes after ionizing radiation or other cytotoxic agents.

The structure and function of the thyroid gland are described. A detailed analysis of population kinetics in the gland suggests a method of measuring cell survival after irradiation that has many features in common with methods used in other mammalian cell systems. This method is used to obtain survival curves for thyroid cells afer irradiation. The effects on survival of splitting the radiation dose into two or multiple fractions, radiation type, and radioprotective agents are also examined. In the light of these data the tolerance of thyroid tissue to radiation exposure under various conditions is discussed. The dosimetry and biological effects of 125I and 131I are described in detail, and compared with X-rays. Radioiodine treatment of thyrotoxicosis is presented in relation to the known biological effects of the isotopes on the gland. Carcinogenic action of ionizing radiations in the thyroid are reviewed with particular reference to the clinical consequences of observations in this field.

Cell proliferation was studied in the intestinal epithelium of mice exposed to fractionated abdominal X-irradiation. Exposures were separated by 12, 24, 48 or 72 hr. Labelled nuclei and mitotic figures per crypt using the crypt squash technique were determined at closely-spaced time intervals (1 to 96 hr) after 1, 2, 3, 5, 7 and 9 exposures. Cell cycle times including estimates of G-1, S, G-2 and M were determined at 12 and 24 hr. These data show that the intestinal epithelium has a remarkable potential to repair damage and recover following severe injury if sufficient time is allowed for the acceleration in proliferative activity. The damage-repair-recovery pattern, i.e., increase in size of proliferative population and acceleration of the generation cycle, is similar for single and fractionated exposures. The number of 300 R exposures which can be tolerated by a highly organized in vivo cell population is dependent upon time interval between fractions; e.g., when interval between fractions is 12 hr eight 300 R exposures kill all animals, but when the interval is increased to 72 hr some animals survive 20 doses, although time of death is highly variable. The compensatory recovery potential is maintained over a large number of exposures.

Atmospheric pollutants that reduce the amount of ozone in the stratosphere may markedly increase the flux of intermediate-wavelength solar ultraviolet (UV) radiation that reaches the Earth's surface. Like short-wavelength germicidal UV radiation (less than 280 nm), these intermediate UV wavelengths (280-315 nm) can promote photochemical reactions in nucleic acids, leading to the appearance of such products as cyclobutadipyrimidines and single- and double-strand breaks. These photochemical reactions strongly affect the biological activities of the nucleic acids. Computer techniques are now available for predicting the chemical and biological effects of increased in vitro irradiation of purified nucleic acids. However, the effect of increased UV irradiation in vivo is complicated by the presence of sensitizing agents in cells and by the action of nucleic acid repair processes. There is strong evidence that in vivo damage to nucleic acids injures irradiated cells and tissues, but further research is needed to predict quantitatively the physiological consequences of increases in solar UV.