Recovery of CFUc in rat bone marrow after prolonged fractionated irradiation with various total doses

The rate and the degree of recovery of committed precursors of granulocytes and monocytes (CFUc) following long-term fractionated irradiation were a function of a cumulative radiation dose. In rats exposed to doses of 9.7 and 19.4 Gy the number of CFUc of myelokaryocytes and granulocytes of blood reached the control values after 1-3 months. The increase in CFUc of animals exposed to a dose of 29.1 Gy was transient and did not provide the recovery of granulocytopoiesis.     

Dependence of the damage and recovery of nucleic acid metabolism on the dose rate in tritium oxide exposure

Disturbance and normalization of nucleic acid metabolism in rat thymus was studied after the effect of tritium oxide delivered in similar cumulative doses but at different dose rates. Both the disturbance and normalization were shown to be a function of dose rate, the slightest damage and the complete recovery being registered at the lowest dose rate (the amount of tritium oxide administered being 0.37 MBq/g/day). The rate of restoration was also a function of dose rate; with tritium oxide dose of 1.85 MBq/g/day (the dose rate at the stage of the equilibrium tritium content in the aqueous phase being 0.38 Gy/day) it was 9 times as high as that after a dose of 0.37 MBq/g/day (0.11 Gy/day dose rate).     

Reaction of mouse hematopoietic stem cells on gamma-irradiation and exposure to tritium oxide

In experiments on 600 mice, relative biological effectiveness of tritium oxide was compared to that of gamma-radiation (137Cs) with respect to the response of CFUc. It was shown that RBE of tritium oxide was 1 within the dose range from 0.8 to 0.4 Gy.     

Relative biological effectiveness of tritium oxide by the criterion of death of the germ cells in mice

It was shown that low-level beta-radiation of tritium is much more effective than gamma-radiation of 137Cs with respect to reduction of the mouse testis weight. The RBE coefficient increases from 1.8 at a dose of 1 Gy to 2.2-2.3 at 0.1 Gy. On the basis of the data obtained by the authors and those reported in the literature a quality factor is proposed for tritium: QF = 2. Using THO and Na36Cl labels a mean water content of the testis cells, necessary for the estimation of a tritium-radiation dose absorbed, has been determined: gamma ct = 0.70 +/- 0.02 ml/g.     

Comparison of the structure and catabolism of rat thymus DNA exposed to tritium oxide and gamma-radiation in equal doses

A decrease in DNA concentration and in the molecular mass of single-stranded DNA, an increase in the PDN content, and activation of acid DNAses in rat thymus were observed after a single administration of tritium oxide in a dose of 22 mBq/g (a cumulative dose of 7.8 Gy) and gamma-irradiation at a corresponding dose-rate and value of the cumulative dose. These changes were most pronounced during the period of dose accretion, i.e. during 14-30 days after the beginning of irradiation. The degree to which the indices under study varied from the controls was 2-3 times in rats given tritium oxide than in those exposed to gamma-irradiation.     

Effect of tritium oxide in a wide range of doses on the nucleic acid metabolism of the rat spleen

A single injection of tritium oxide in a dose of 1.1 MBq/g (0.5 Gy for 30 days) was shown to impair the nucleic acid metabolism in the rat spleen. The changes in the indices under study (e.g. mass, nucleic acid content and biosynthesis) increased with the dose, and the recovery started later and was incomplete. Qualitative differences were found in the effects of tritium oxide and gamma radiation with regard to the rate of DNA biosynthesis: 24 h following the injection of the radionuclide specific activity of DNA increased with dose, whereas this function was inverse in the case of gamma irradiation as it was reported in the literature.     

Normal killer function in CBA mice as affected by long-term intake of tritium oxide

A study was made of the cytotoxic function of normal killers of CBA mice during long-term administration of tritium oxide in potable water (a cumulative absorbed dose of 8.7 Gy, dose-rate, 4.5 Gy/day) and at different times after termination of the radionuclide injection. A mean decrease of 20-30% in the lytic effect of the effectors from spleen of the experimental mice on cell-targets of K-562 human erythroleukosis was demonstrated by a 17-19-hour test with 51Cr. At later times after termination of action of tritium oxide, the cytotoxic effect of normal killers increased by 1.8 times as compared to intact controls of the same age.     

Estimation of relative biological effectiveness of tritium according to chromosome aberration frequency in human blood lymphocytes

The goal of this work was to determine the relative biological effectiveness (RBE) of tritium β-radiation according to the chromosome aberration frequency in the peripheral blood lymphocytes after in vitro and in vivo radiation exposures. The experimental RBE assessment of tritium β-radiation relative to ⁶⁰Co γ-radiation according to unstable chromosome aberration frequency in the peripheral blood lymphocytes under particular conditions is described. It has been demonstrated that tritium β-radiation is, in general, more effective in the dose range of up to 1 Gy, which is most pronounced at low doses. The RBE value of tritium β-radiation at minimum doses reached 2.2 and decreased at higher doses (1 Gy) to 1.25. The data on comparative analysis of the frequency of stable chromosome aberrations in the blood lymphocytes of professional nuclear workers (Sarov, Russia) after long-term chronic exposure to tritium β-radiation, as compared with γ-irradiation, are reported for the first time. The higher biological effectiveness of tritium β-radiation was demonstrated and was estimated as 2.5.     

The early changes in humoral immunity under the prolonged action of tritium oxide with different dose rates

Within the dose range from 0.2 to 1 Gy, early changes in the humoral immunity of mice exposed to tritium oxide at varying dose rates have been investigated. The study of the immunity impairment at different stages of immunopoiesis permits to reveal the points (a lymphocyte precursor department) that are mostly affected by radiation, to find the causes of the decrease in the antibody production, and to reveal the relationship between the damages observed the dose absorbed and dose rate of beta radiation.     

The frequency of chromosome aberrations in rat bone marrow cells in the late period after a single uptake of tritium

A prolonged self-maintenance of haemopoietic tissue cells with stable chromosome rearrangements following a single intake of tritium oxide in the amount of 24 MBq/g of body weight (absorbed dose of 11 Gy) is shown. Mutant cells revealed long after the radionuclide exposure are descendants of stem-cell precursors, bearing stable chromosome aberrations during the period of formation of radiation injury after the radionuclide administration.     

The recovery of humoral immunity after the long-term action of tritium oxide at different irradiation levels

Dynamics of recovery of humoral immunity of CBA mice was studied 1, 3, 6 and 12 months after termination of long-term exposure to tritium oxide at various levels of absorbed doses (3, 5 and 9 Gy) and dose rates (3.3, 4.9 and 9.2 cGy.day-1). A severer and more stable residual radiation damage was observed in the department of lymphocyte precursors. A considerable decrease in the content of antibody producers was due to the lymphoid tissue hypoplasia. There was a direct relationship between the immunodeficiency and dose rate and total absorbed dose of beta radiation.     

Mutation induction by tritiated water and effects of deuterium oxide in cultured mouse leukemia cells

Induction of mutation to 6-thioguanine resistance was studied in L5178Y mouse leukemia cells after exposure to low-dose-rate gamma rays or tritiated water at dose rates of approximately 0.025 to 0.4 Gy/hr for 20 hr in the presence or absence of 45% (v/v) deuterium oxide. The effect of acute gamma-ray exposure was also examined. A higher frequency of induced mutations was observed after tritium beta rays than after gamma rays, both at equivalent doses and cell survival. Deuterium oxide enhanced the mutation induced by gamma rays and tritium beta rays but did not affect the survival-mutation correlation of the two radiations.     

Cloning of murine B- and T-lymphocytes in vitro after the long-term action of tritium oxide

The cloning method was used to study the content of B- and T-lymphocyte committed precursors in central and peripheral organs of the immune system of mice at different times after long-term exposure to tritium oxide (a cumulative dose of approximately 9 Gy). It was shown that recovery of the colony-forming ability of the committed lymphocyte precursors was different in central and peripheral lymphoid organs; the dynamics and degree of restoration of the pools of B--(CFU--LB) and T--(CFU--LT) lymphocyte precursors were different.     

Occurrence of mammary tumors in rats after exposure to tritium beta rays and 200-kVp X rays

The RBE for tritium was estimated in reference to 200-kVp X rays, using acceleration of breast tumor appearance in the female Sprague-Dawley rat as the end-point. Chronic X-ray doses of 0.3-2.0 Gy were delivered over 10 days. Intraperitoneal injections of tritiated water ranging in concentrations from 45 to 370 MBq/100 g body wt were administered, followed by four additional injections at 2-day intervals and half of the initial concentrations. Seventy-five percent of the total tritium dose was delivered to the mammary gland within the first 10 days and 95% within the first 20 days after the start of the tritium exposure. RBE estimations were based on various criteria including the tumor incidence per Gy at 450 days postirradiation and the time required to induce tumors in 50% of the animals at risk. The results suggest that tritium beta rays are about 1.1-1.3 times more effective than chronic 200-kVp X rays for acceleration of the appearance of rat mammary tumors. However, the uncertainties involved in these calculations are such that the effects of tritium beta rays could not be reliably distinguished from those of chronic 200-kVp X rays. Measured differences in RBE values were slightly larger for the comparison between acute and chronic X rays than for the comparison between chronic tritium beta rays and chronic X rays.     

A mathematical model of the dynamics of granulocytopoiesis in mammals

A mathematical model has been developed for the dynamics of granulocytopoiesis in mammals subjected to chronic irradiation. The model involves a chalones mechanism of haemopoiesis regulation and comprises 12 nonlinear differential equations. The simulation results agree with the experimental data concerning the dynamics of granulocytopoiesis in rats affected by radiation within a wide range of dose rates.     

Assessment of relative biological effectiveness of tritium using chromosome aberration frequency in human blood lymphocytes

The aim of this work is to determine Relative Biological Effectiveness (RBE) of tritium beta-irradiation using chromosome aberration frequency in peripheral blood lymphocytes after radiation exposure in vitro and in vivo. The results of the experimental estimation of tritium beta-irradiation RBE in comparison with 60Co gamma-irradiation using analysis of unstable chromosome aberration frequencies in peripheral blood lymphocytes in reference to concrete conditions of the investigation were presented. It was demonstrated that tritium beta-irradiation is in total more effective than gamma-irradiation up to 1 Gy. RBE of tritium beta-irradiation was determined as 2.2 at minimum doses and decreased at higher doses (1 Gy) up to 1.25. For the first time results of the comparative analysis of frequencies of stable chromosome aberrations in two groups of professional nuclear workers (town Sarov) exposed to chronic tritium beta- and gamma-irradiation in remote period were presented. The grater RBE of tritium beta-irradiation was demonstrated. It has been estimated as 2.5.     

The immunity indices of rats after the long-term action of tritium oxide or gamma irradiation

In experiments with Wistar rats, a study was made of the content of antibody-forming cells and cytotoxic activity of normal killers after long-term administration of tritium oxide (3HOH) (370 kBq.g-1 of body mass daily, cumulative dose, 8.1 Gy, and dose rate, 8.5 cGy/day), and after gamma irradiation with corresponding doses. The long-term radiation effect caused a decrease in the immunity indices: the impairment of the immune reactions was more pronounced after the effect of 3HOH than after gamma irradiation. Damages to the immune system of mice and rats after irradiation with similar doses were compared.     

Inactivation of non-syngeneic hematopoietic stem cells by mouse lymphocytes after long-term exposure to tritium oxide

A study was made of functional activity of lymphocytes, which inactivated nonsyngeneic colony-forming units (CFU) in allogenous and xenogenous interaction systems, at different times after long-term action of tritium oxide in a cumulative dose of approximately 9 Gy. The function of these lymphocytes was depressed during the first months after termination of exposure while at later times it exceeded the control level. The consequences of the interaction between lymphocytes and nonsyngeneic CFU were also studied in this work.     

The significance of immunity disorders in the development of tumorous effects during the long-term action of tritium in mice

In experiments with CBA mice it was shown that the long-term influence of tritium oxide administered with drinking water daily during 180 days (370 kBq.g-1 of body mass, cumulative dose 8.7 Gy, dose rate 4.5 cGy.day-1) causes the development of immunity deficiency 90 days after the onset of the administration that persists for up to 270 days. There is a 34% decrease in the average life of irradiated animals and an increase in the number of malignant neoplasms (postmortem examination was performed after natural death or killing on days 250, 350 and 450). There is a direct relationship between the occurrence of malignant neoplasms and the immunity deficiency.     

Estimated yield of double-strand breaks from internal exposure to tritium

Internal exposure to tritium may result in DNA lesions. Of those, DNA double-strand breaks (DSBs) are believed to be important. However, experimental and computational data of DSBs induction by tritium are very limited. In this study, microdosimetric characteristics of uniformly distributed tritium were determined in dimensions of critical significance in DNA DSBs. Those characteristics were used to identify other particles comparable to tritium in terms of microscopic energy deposition. The yield of DSBs could be strongly dependent on biological systems and cellular environments. After reviewing theoretically predicted and experimentally determined DSB yields available in the literature for low-energy electrons and high-energy protons of comparable microdosimetric characteristics to tritium in the dimensions relevant to DSBs, it is estimated that the average DSB yields of 2.7 × 10(-11), 0.93 × 10(-11), 2.4 × 10(-11) and 1.6 × 10(-11) DSBs Gy(-1) Da(-1) could be reasonable estimates for tritium in plasmid DNAs, yeast cells, Chinese hamster V79 cells and human fibroblasts, respectively. If a biological system is not specified, the DSB yield from tritium exposure can be estimated as (2.3 ± 0.7) × 10(-11) DSBs Gy(-1) Da(-1), which is a simple average over experimentally determined yields of DSBs for low-energy electrons in various biological systems without considerations of variations caused by different techniques used and obvious differences among different biological systems where the DSB yield was measured.