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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 Raji cells, it has been shown that the serum growth factors activate the growth of gamma-irradiated (0.36 mGy/day) culture. The authors discuss the role of radiation stimulation of membrane receptors in recepting natural effectors.

Chronic exposure of rat pups to gamma radiation, during their intensive growth, at a dose rate of 0.01, 0.11 and 0.5 cGy/day did not affect their development throughout a two-month period of observation. At a dose rate of 12.9 cGy/day rat growth was inhibited during the first 15 days. With further exposure at the same dose rate (over a period of up to five months) the rate of rat pup growth was restored, which indicated the presence of adaptation processes.

Sorption by SKN-2M coal of various endogenous substances, including quinones (tyrosine oxidation products) and quinoid radiotoxins (QR) isolated from gamma-irradiated plant and animal tissues has been studied. The fact that the precursors of QR-DOPA, tyrosine and QR, isolated from gamma-irradiated plant and animal tissues, are readily absorbed by the sorbent under study supports the major contribution of QR removal from the organism to the therapeutic effect of hemosorption after gamma irradiation of animals with minimal lethal doses.

Ornithine decarboxylase activity changes in some tissues of chronically gamma-irradiated rats (0.54 cGy/h). The radiation effect is a function of the life span of continuously exposed animals. The data obtained indicate that adaptation is possible, at a metabolic level, with the restricted chronic gamma-irradiation of animals.

A study was made of the response of adenylate cyclase of cytoplasmic membranes of pulmonary tissue to chronic gamma irradiation of rats at a low-dose rate (0.036 cGy/day). The adenylate cyclase complex receptors were shown to respond to such exposure by activation of the enzyme they control and by being more sensitive to their specific effector, isoproterenol. The role of receptors in the manifestation of radiation hormesis is discussed.

A study was made of the activity of adenylate cyclase and cAMP-phosphodiesterase in rat thymus and liver various time intervals following nonlethal fractionated gamma-irradiation (2 Gy three times at a week interval). There was a positive correlation between the activity of cAMP metabolism enzymes and the radiation modification of ornithine decarboxylase (ODC) observed before. It is suggested that cAMP system is involved in ODC activity regulation in the exposed tissue.

Development of rat pups was shown to accelerate (body mass made up 121% of control) after gamma-irradiation on day 21 of the postnatal development (2.88 cGy, dose-rate of 0.12 cGy/h). Higher cumulative doses (14.4 and 144 cGy) did not influence the body mass growth, and inhibition was only caused by doses exceeding 150 cGy.

Gamma-irradiated serum albumin activated L-tyrosine oxidation to 3,4-dioxyphenyl alanine (DOPA) and forms adducts with DOPA oxidation products. These adducts are more resistant to proteolysis and have bactericidal and mutagenic capacity. A possible role of such adducts in a radiation damage to the organism is discussed.

The radiobiological studies carried out in conditions of lower and slightly increased natural radiation background have prompted an idea of "low doses" in radiobiology which is proposed for discussion. The author emphasizes that the difference between the leading molecular and cellular mechanisms that come into play under the effect of high- and low-level atomic radiation makes it incorrect to assess the risk from low radiation doses on the basis of the regularities obtained with high doses.

Basal and stimulated activity of adenylate cyclase (cyclizing ATP-pyrophosphate lyase, E.C. 4.6.1.1., AC) in plasma membranes of pulmonary tissue was being studied during a year after fractionated irradiation of rats (2 GyX3). Basal and hormone-stimulated activity of AC was shown to vary significantly from normal 6 and 12 months after irradiation. The exposed membranes responded differently to AC activation by isoproterenol and F-.

Protective and therapeutic effect of ubiquinone-8 was demonstrated on rats exposed to 8 Gy radiation. There was a 16-20% increase in the survival rate of the irradiated rats as compared with the controls. The per os administration of ubiquinone-8 during a five-month period in conditions of chronic exposure arrested the radiation-induced accumulation of lipids in rat liver and somewhat improved the dynamics of the body mass growth in the exposed rats.

In addition to the growth of low molecular weight quinoid radiotoxins the toxic effects of albumin were registered in rat plasma 4-24 h following gamma-irradiation. It is assumed that adducts of albumin with quinoid radiotoxins are formed and contribute to the development of radiation injury to critical organism tissues.

It was shown that gamma-radiation-induced oxidation of phenol compounds in the animal liver, which leads to o-dioxyphenols and quinones accretion, is one of the reasons for excluding cytochrome c from the respiratory chain of mitochondria. Radiochemical oxidation of tyrosil groups at the protein site of cytochrome c and, as a result, the restriction in the rate of reduction of the latter were noted. On the basis of the data obtained the authors discuss the mechanism of weakening the coupling of oxidation to phosphorylation upon irradiation and the molecular mechanism of the so-called cytochrome effect.

A decrease in the induced synthesis of glucokinase in the liver, at the time of spontaneous appearance of the enzyme, was observed in suckling rats kept for 10 days in a chamber with a decreased (by 10 times) natural radiation background. No changes were noted in the glucokinase synthesis induction after restoration of natural radioactivity by introducing of uranium salts.

In the in vitro experiments with lymphoid cells Raji and X63-Ag8.653 gamma-irradiated in a synthetic medium, it was shown that a cessation of division (reproductive death) and lysis (interphase death) of cells were evoked by the abscopal effect of long-lived quinoid radiotoxins enhancing the direct effect of radiation to make it not additive but synergistic: a synergism coefficient was 1.3.

In experiments with a suspension culture of human Raji lymphoid cells it was shown that a 40 per cent deceleration of the population growth induced by 2.5 Gy gamma-radiation persisted within the following 15-16 generations, afterwards it gradually normalized to reach the control level in the 21st generation. However, the incompleteness of recovery was displayed with the repeated exposure and cultivation of cells under hyperthermia (40 degrees C) up to the 27th generation.

Evidence was obtained that beta-carotene injected to rats subcutaneously or per os two times, 4 h and 19 h, before irradiation reduced their death rate from acute affection. The effect was almost invariable with the drug administered either before or after irradiation. The radioprotective efficacy of beta-carotene was attributed to its ability to scavenge active oxygen forms.

The initial steps of radiation carcinogenesis have been briefly surveyed. Actuality of their further research is shown on the molecular level. There is a discussion going on about the close connection of such research with basic directions in the development of biology, such as: genome destabilization, gene repression and activation, regulation of growth activity factors, the role of biomembranes in the processes, and synergism in the action of factors on live systems.

Ornithine decarboxylase activity in some rat tissues was shown to grow at remote times after gamma irradiation (60Co) with nonlethal doses. The authors suggest that ornithine decarboxylase activity should be used as a biochemical marker of remote effects of ionizing radiation.

In experiments with model plant tumors (Kalanchoe-ti plasmid Agrobact. tumefaciens C-58D) it was shown that exposure of the recipient plant to low-level gamma-radiation of 2 Gy induced changes in cells that were not repaired over two months promoting tumoral transformations in them. Those changes were shown to persist in the offspring of the exposed somatic cells.

It was established that quinoid products of tyrosine oxidation, analogues of natural radiotoxins, when used in the studied doses decreased the radiosensitivity of spleen stem cells and enhanced the restoration of bone marrow cellularity of mice exposed to sublethal gamma-radiation doses.

A considerable increase in the lethal effect of gamma-radiation on mice was noted after postirradiation administration of nontoxic quantities of quinoid radiotoxins (synergism). The same synergistic effect was observed on human lymphoid cells Raji in culture.

Gamma irradiation of a grain during embryogenesis at an intensity only 100 times exceeding that of the natural radioactive background reduces by 4-7 h the average time of embryogenesis for different species and hybrids of thesilworm embryo. The 10- and 40-time increase in the radiation intensity decreases the stimulatory effect and leads to the delay in the development.

Chronic gamma-irradiation of an egg at a dose-rate 100, 1000 and 4000 times as high as that of the natural radiation background significantly accelerates the development of Bombyx mori L. The caterpillar development may also be stimulated by a single exposure of the egg to 2 Gy radiation. The acceleration of the caterpillar growth promotes the increase in the cocoon weight and the raw-silk mass.

Quinoid radiotoxins were found in the peripheral blood 3-4 h following gamma-irradiation of dogs with doses of 5.76 Gy. The authors developed a simple method of isolation and purification of quinoid radiotoxins and specified their physicochemical and biological characteristics.

A study was made of the rate of the transfer of phospholipids and cholesterol between 14C-microsomes and mitochondria of gamma-irradiated rat liver. Cytosole and cell organelles of nonirradiated and irradiated rat liver were combined to reveal the increase in the cholesterol-transfer activity of liver cell cytosole 60 min following irradiation (12 Gy). Roughly purified lipid-transfer proteins from liver cytosole of control rats transported lipids, at an equal rate, between organelles isolated from liver cells of control and exposed rats. Radiation modification of cell organelle membranes was only detected upon the reaction with cytosole from the irradiated rat liver.