Radiobiologiia最新文献

There are some genes whose expression increases in non-proliferating hepatocytes after whole-body X-irradiation. We suppose that some of them participate in cell division regulation. To verify our postulate we have studied expression of autonomously replicating sequence pDARC1 in normal, irradiated and dividing rat hepatocytes. We have succeeded earlier in cloning the autonomously replicating sequence pDARC1 and have shown that it could be transcribed in X-irradiated hepatocytes. Here we report on the results of analysis of this sequence expression in dividing mammalian cells. Hybridization with the pDARC1 sequence reveals 4.0 kb mRNA in non-proliferating rat hepatocytes after X-irradiation: this mRNA is absent in normal hepatocytes. Induction of 4.0 kb mRNA is a function of radiation dose; 4.0 kb mRNA content is maximum 6-24 h following whole-body 6 Gy X-irradiation. The 4.0 kb mRNA is also found in dividing rat hepatocytes during the pre-replicative period.

Considerable changes in concentrations of cAMP and cGMP and in the CAMPOcGMP ratio were found in the thymus and blood plasma of rats subjected to long-term irradiation at cumulative doses of 10 to 20 Gy. This might be a manifestation of adaptation reactions that develop in response to the effect of ionizing radiation.

Radioprotective agents are divided in 3 groups: (1) cystamine, AET, cystaphos, gammaphos, and thiogammaphos with ED50 (the dose that gives a half of the maximal protective effect) of 10(3)-10(1.6) mumol/kg and therapeutic index K = LD50/ED50 = 10(0)-10(1.6); (2) 5-methoxytryptamine, phenylephrine, serotonin, and norepinephrine with ED50 = 10(1)-10(0) mumol/kg and K = 10(1.8)-10(2,6); (3) clonidine and isoprenaline with ED50 = 10(-0.5)-10(-0.8) mumol/kg and K = 10(3)-10(4). Possible causes of these differences and advantages of low ED50 and high K are discussed.

Comparative studies were made of immediate (within the first minutes) changes in intracellular ATP concentration after irradiation by different regimens. ATP concentration in cells at a stationary phase of growth increased immediately after irradiation with a dose of 5 Gy, reaching its maximum within 30-40 min. Irradiation with the same total dose, by the regimen of 0.1 + 4.9 Gy at a 3-minute interval between the doses, did not cause alterations in the ATP content in cells. It is concluded that the absence of the increase in the parameter under study (ATP) after irradiation by the latter regimen indicates that preirradiation at a dose of 0.1 Gy inhibits the adequate development of an early response to irradiation with a dose of 4.9 Gy.

The influence of external single gamma-irradiation with a dose of 1 Gy on the isoenzyme composition of lactate dehydrogenase, malate dehydrogenase, esterase and acid phosphatase in the cytoplasm of rat brain cells has been investigated. Irradiation was shown to cause differently directed changes in the ratio of the isoenzymes under study at different times after exposure. The isoenzyme spectrum of lactate dehydrogenase and malate dehydrogenase was shown to be normalized on day 30 after irradiation, whereas the isoform composition of esterase and acid phosphatase was not stabilized at that time.

Different phase changes were observed in adenylate cyclase (AC) activity of pulmonary tissue plasma membranes under chronic gamma-irradiation of rats at a dose-rate of 12.9 cGy/day. Comparison of AC basal activity with the data reported earlier on changes in ornithine decarboxylase activity under similar radiation conditions showed unidirectional changes which indicated that cAMP-dependent processes were possibly involved in radiation modification of ornithine decarboxylase.

In experiments with models of isogenic Escherichia coli strains, a comparative study was made of the effect of SHF of electromagnetic field and hyperthermia. The survival rate of bacteria was determined and, simultaneously, injuries to genetic supramolecular structures were registered through measuring the anomalous time dependence of cell lysate viscosity. The combined effects of the mixture of these factors with H2O2 microconcentrations were studied. The differences observed in their realization were attributed to the different mechanisms of action of these factors on the repair enzyme systems of the studied cells. It has been found that the effect of microwaves on microorganisms causes much severer damages to DNA that hyperthermia does.

A comparison was made of the biological effect on mice of irradiation at different dose rates (70, 5.5 and 1.5 cGy/min) with equally effective, with respect to lethality, doses, or with physically equal doses within the range from 1/4 of LD50/30 to LD99-95/30. Equally effective, with respect to lethality, doses caused similar changes in the intestinal epithelium and in the haemopoietic system. The death rate kinetics was identical with doses of LD80-95/30 within the dose-rate range under study. The equally effective doses caused injuries, different in degrees, to critical systems, including CFUs.

On the basis of the literature the necessity of using not only DMF and maximal protective or sensitizing effects, but also the affinity and the range of the pharmacological action of radiation modifiers is argued. The affinity is worth while to expressed as ED50 (the dose that produces a half of the maximal effect), and the range of the pharmacological action as a therapeutic index K = LD50/ED50.

A generalized multihit-multitarget model for a nonhomogeneous, with respect to radiosensitivity, population of irradiated cells is presented. The least squares and the maximum likelihood estimation of the model parameters is given. The estimates quality is evaluated by the computer-based study. The results obtained show the possibility of the parametric identification of cell radiosensitivity distribution according to the "dose-response" data.