Psychophysiological development of two generations of female rats chronically exposed to gamma-irradiation during pregnancy in the total dose of 1 Gy and its modification by melanin

The purpose of the work was to study the embryotoxic action of chronic gamma-irradiation of pregnant female rats (F0) during the first 10 days of pregnancy in the total dose of 1 Gy (mean dose rate of 5.31 mGy/hour) on psychophysiological development of posterity of the first (F1) and the second (F2) generations and its modification by natural pigment melanin (peroral 10 mg/kg once per day during the irradiation). 54 pregnant female Wistar rats were the objects of research were their 180 descendants of the first generation and about 400 descendants of the second generation of maternal and of paternal lines. Psychophysiological development and its correction by melanin estimated on ability to learning with the test of training a conditioned avoidance reflex in the shuttle box. Precise negative action of gamma-irradiation in the aforesaid dose on psychophysiological development of posterity of the first generation is established. At rats of the second generation the inferiority is shown mainly at descendants of maternal line. Application of melanin of natural origin in most cases diminished negative consequences of the irradiation.     

The influence of the exogenous melanin on the development of the second generation of the female Wistar rats exposed during the critical period of the pegnancy at the nonsterilizing doses of different rate means

The purpose of this study was to estimate the radio-protective activity of melanin for the reproductive status of Wistar rats. Wistar rats were exposed in utero either to the single gamma-irradiation on the tenth day of embryogenesis with the dose of 1 Gy or to the chronic gamma-irradiation with the total dose of 1 Gy during the first 10 days of embryogenesis. Such things like the ability of the rats to conceive, the embryogeny and early postnatal ontogeny of rat's posterity were studied. These doses of the radiation and the melanin did not produce the significant damages of the reproductive function of the survival offsprings of the first generation. The possible mechanisms of radio-protective effect of melanin on reproductive system of animals which have been exposed with the nonsterilizing doses at different mean dose rate were discussed.     

Activation of the DNA repair system in tissues of mice subjected to chronic gamma irradiation

Mice exposed to gamma-quanta during 47 and 82 days at a dose-rate of 1.3 mGy/h and cumulative doses of 1.45 and 2.54 Gy, respectively, were subsequently subjected to a single acute irradiation with a dose of 20 Gy. Repair of DNA damages induced by the acute exposure was shown to proceed in the brain, pulmonary and splenic tissues of chronically exposed mice more readily than in the tissues of mice not subjected to chronic irradiation. The data obtained indicate that the induced adaptive response activates DNA repair in tissues of mice exposed to long-term low-level radiation.     

Mitochondrial DNA mutation frequencies in experimentally irradiated compost worms, Eisenia fetida

The compost worm Eisenia fetida is routinely used in ecotoxicological studies. A standard assay to assess genetic damage in this species would be extremely valuable. Since mitochondrial DNA (mtDNA) is known to exhibit an increased mutation rate following exposure to ionising radiation we assessed the validity of a mtDNA-based assay for measuring increases in mutation rate in laboratory-irradiated compost worms. To this end the mutation frequency in the mtDNA of the compost worm E. fetida was quantified following in vivo gamma-irradiation of adult worms in three dose groups. Five adult worms exposed to 1.4 mGy/h for 55 days (total dose 1.85 Gy), five adult worms exposed to 8.5 mGy/h for 55 days (total dose 11.22 Gy) and five adult control worms were used to assess the effect of irradiation on mtDNA mutation induction. DNA samples extracted from irradiated adult worms were used in high-fidelity PCR of a 486 bp region of mtDNA spanning the ATPase 8 gene, chosen for its high spontaneous mutation rate. PCR products were cloned and sequenced to identify mutations, with 89-102 clones successfully sequenced per individual. A significant elevation in mtDNA mutation frequency (p=0.032) was seen in worms exposed at the higher dose rate (8.5 mGy/h, total dose 11.22 Gy; mutation frequency 27.98+/-4.85 x 10(-5)mutations/bp) in comparison to controls (mutation frequency 12.68+/-3.06 x 10(-5)mutations/bp), but no elevation in mutation frequency (p=0.764) was seen for the lower dose rate (1.4 mGy/h, total dose 1.85 Gy; mutation frequency 13.74+/-1.29 x 10(-5)mutations/bp) compared with controls. This indicates that although the technique has the potential to detect an elevation in mutation frequency, it does not have sufficient sensitivity at the doses likely to be encountered in environmental monitoring scenarios.     

Increase in the activity of nuclear DNA polymerases in the tissues of mice subjected to long-term gamma irradiation

Activity of nuclear DNA-polymerase in the liver, lung and spleen tissues of mice subjected to long-term chronic gamma-irradiation (1.3 mGy/h) has been investigated. Chronic gamma-irradiation with a cumulative dose of 1.7 Gy during 55 days raises DNA polymerase activity in the irradiated tissue nuclei. Analysis of DNA-polymerase activity in the liver nuclei have demonstrated that this increase is connected with activation of DNA-polymerase beta.     

Estimation of the levels of radiation-induced P-element transposition in Drosophila melanogaster experimental populations and laboratory strains

When experimental P + M populations were exposed to chronic gamma-irradiation (0.31 mGy/h), the highest instability level of the singed-weak (sn(w)) locus was observed in F3-F10 with a subsequent decrease and stabilization of the mutation rate. The sn(w) mutation rate was within the range of spontaneous variation in conditions of P-M hybrid dysgenesis and irradiation of males of the Harwich laboratory strain with active P elements at 1.61 mGy/h. The instability of the sn(w) locus was significantly higher at lower dose rates (0.23 and 0.31 mGy/h), suggesting a nonlinear dose-effect relationship.     

Mathematical Modeling Predicts Enhanced Growth of X-Ray Irradiated Pigmented Fungi

Ionizing radiation is known for its cytotoxic and mutagenic properties. However, recent evidence suggests that chronic sub-lethal irradiation stimulates the growth of melanin-pigmented (melanized) fungi, supporting the hypothesis that interactions between melanin and ionizing photons generate energy useful for fungal growth, and/or regulate growth-promoting genes. There are no quantitative models of how fungal proliferation is affected by ionizing photon energy, dose rate, and presence versus absence of melanin on the same genetic background. Here we present such a model, which we test using experimental data on melanin-modulated radiation-induced proliferation enhancement in the fungus Cryptococcus neoformans, exposed to two different peak energies (150 and 320 kVp) over a wide range of X-ray dose rates. Our analysis demonstrates that radiation-induced proliferation enhancement in C. neoformans behaves as a binary “on/off” phenomenon, which is triggered by dose rates <0.002 mGy/h, and stays in the “on” position. A competing dose rate-dependent growth inhibition becomes apparent at dose rates >5000 mGy/h. Proliferation enhancement of irradiated cells compared with unirradiated controls occurs at both X-ray peak energies, but its magnitude is modulated by X-ray peak energy and cell melanization. At dose rates <5000 mGy/h, both melanized and non-melanized cells exposed to 150 kVp X-rays, and non-melanized cells exposed to 320 kVp X-rays, all exhibit the same proliferation enhancement: on average, chronic irradiation stimulates each founder cell to produce 100 (95% CI: 83, 116) extra descendants over 48 hours. Interactions between melanin and 320 kVp X-rays result in a significant (2-tailed p-value = 4.8×10⁻⁵) additional increase in the number of radiation-induced descendants per founder cell: by 55 (95% CI: 29, 81). These results show that both melanin-dependent and melanin-independent mechanisms are involved in radiation-induced fungal growth enhancement, and implicate direct and/or indirect interactions of melanin with high energy ionizing photons as an important pro-proliferative factor.     

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.     

Dose-response relationship for translocation induction in spermatogonia of the crab-eating monkey (Macaca fascicularis) by chronic gamma-ray-irradiation

The induction of reciprocal translocations in spermatogonia of the crab-eating monkey (Macaca fascicularis) by chronic gamma-irradiation (1.8 x 10(-5) Gy/min, about 0.024 Gy/22 h/day) was examined. The frequencies of translocation per cell were 0.15% at 0.3 Gy, 0.27% at 1.0 Gy and 0.33% at 1.5 Gy. The dose-response relationship for translocation yield was a linear one with a regression coefficient (b) of 0.16 x 10(-2). When the slope (b) of the regression line was compared with that at a high dose rate (0.25 Gy/min, b = 1.79 x 10(-2), it was clear that the induction rate of translocations after chronic gamma-irradiation was only about one-tenth of that after high-dose-rate irradiation. Thus, there was evidence for a pronounced dose-rate effect in the crab-eating monkey.     

Mutation induction by very low dose rate gamma rays in cultured mouse leukemia cells L5178Y

Induction of cell killing and mutation to 6-thioguanine resistance was studied in growing mouse leukemia cells in culture following gamma rays at dose rates of 30 Gy/h, 20 cGy/h, and 6.3 mGy/h, i.e., acute, low dose rate, and very low dose rate irradiation. A marked increase was observed in the cell survival with decreasing dose rate; no reduction in the surviving fraction was detected after irradiation at 6.3 mGy/h until a total dose of 4 Gy. Similarly, the induced mutation frequency decreased after low dose rate irradiation compared to acute irradiation. However, the frequency after irradiation at 6.3 mGy/h was unexpectedly high and remained at a level which was intermediate between acute and low dose rate irradiation. No appreciable changes were observed in the responses to acute gamma rays (in terms of cell killing and mutation induction) in the cells which had experienced very low dose rate irradiation.     

Suppression of thymic lymphoma induction by life-long low-dose-rate irradiation accompanied by immune activation in C57BL/6 mice

The induction of thymic lymphomas by whole-body X irradiation with four doses of 1.8 Gy (total dose: 7.2 Gy) in C57BL/6 mice was suppressed from a high frequency (90%) to 63% by preirradiation with 0.075 Gy X rays given 6 h before each 1.8-Gy irradiation. This level was further suppressed to 43% by continuous whole-body irradiation with 137Cs gamma rays at a low dose rate of 1.2 mGy/h for 450 days, starting 35 days before the challenging irradiation. Continuous irradiation at 1.2 mGy/h resulting in a total dose of 7.2 Gy over 258 days yielded no thymic lymphomas, indicating that this low-dose-rate radiation does not induce these tumors. Further continuous irradiation up to 450 days (total dose: 12.6 Gy) produced no tumors. Continuously irradiated mice showed no loss of hair and a greater body weight than unirradiated controls. Immune activities of the mice, as measured by the numbers of CD4+ T cells, CD40+ B cells, and antibody-producing cells in the spleen after immunization with sheep red blood cells, were significantly increased by continuous 1.2-mGy/h irradiation alone. These results indicate the presence of an adaptive response in tumor induction, the involvement of radiation-induced immune activation in tumor suppression, and a large dose and dose-rate effectiveness factor (DDREF) for tumor induction with extremely low-dose-rate radiation.     

Characteristics of the descendants of male dogs exposed to chronic combined gamma-irradiation and in the postradiation period

A study was made of the descendants of 12 male dogs subjected to gamma-irradiation during six years at dose-rates of 0.0034 Gy/day and 0.0017 Gy/day + additional annual exposures to gamma-radiation three times a year each of 0.42 Gy. The observations were made during 3 years after the end of irradiation. It was shown that the descendants reflected the regularities of the disorders revealed in fathers' spermatogenesis. The radiobiological effects were function of dose--rate and cumulative radiation dose. The changes were mainly noted during embryogenesis and manifested by the sterility, mortinatality and the decreased number of puppies in the postreity.     

Effect of external irradiation with different intensity at 1 Gy dose on the DNA, RNA and total protein content in the testis and liver of rats

The content of DNA, RNA and total protein in the rat testes and liver was studied 1 and 30 days after external chronic gamma-irradiation (dose rate 1.8 and 5.76 cGy/day) and acute gamma-irradiation with relatively low dose rate (5.4 cGy/min) up to a total dose of 1 Gy. The results obtained pointed to the specific metabolic reaction of radiosensitive (testes) and radioresistant (liver) tissues of organism at external irradiation at relatively low dose of different intensity due to unequal cell capacity for proliferation.     

Mutagenic effect of cyclophosphan on bone marrow cells of irradiated rats]

The rate of chromosome aberrations in bone marrow cells of male rats was investigated in 24 hours after the cyclophosphan intraperitoneal injection (25 mg/kg). Cyclophosphan was given to rats exposed earlier (15 days, 1, 3, 4, 6 or 9 months before) to X- and gamma-irradiation (400 rads). It was found that preliminary irradiation led to the increase in the mutagenic effect of cyclophosphan as compared to that obtained for intact rats. This effect was demonstrated during 4 months after acute X-irradiation at a dose rate of 70 rads/min and during 1 month after chronic gamma-irradiation at a dose rate of 100 rads/day. Later the effect was shown to disappear in both cases. Chronic irradiation was found to be less efficient in the stimulation of chromosome damages caused by chemical mutagens. The increase of the mutagenic effect of cyclophosphan resulted in the increase of both the number of cells carrying chromosome breaks and the severity of a damage per cell. Different ways of the irradiation effect on the mutagenic action of chemicals are discussed.     

Experimental study of the radioprotective action of melanin on the somatic development during irradiation in the antenatal period of ontogenesis

Daily introduction per os of the exogenous melanin in a doze of weight of 10 mg/kg pregnant female rats Wistar eliminated the functional deficiency of somatic development revealed at posterity at chronic gamma-irradiation in a doze 1.00-1.25 Gy for all period of pregnancy. The irradiation or introduction melanin antenatal to a phase ontogenesis resulted in stimulation of the immune answer, which was determined at offspring on 3rd week after birth. On the basis of the received data it is concluded presence radioembryoprotective actions melanin in the relation embryotoxic effects of small dozes of ionizing radiation and its participation in regulation immunogenes.     

Synthetic activity of rat blood lymphocytes under acute and continuous gamma-irradiation – fluorescent microspectral study

The effects of different doses of acute and continuous gamma-irradiation on the synthetic activity of rat blood lymphocytes stained with acridine orange were studied by fluorescent microspectrometry. Male rats were exposed to acute gamma-irradiation with doses of 7.5, 4 and 3 Gy, or to continuous irradiation with dose rates of 14.4, 2.1, 1.1 and 0.43 cGy/day, respectively. The changes of the synthetic activity of blood lymphocytes occurred in three main stages after acute gamma-irradiation and in four stages under continuous irradiation. The stages reflect the processes of depression and activation of the immune system under irradiation. Essential differences between the acute and continuous effects were observed in the first stage. After acute gamma-irradiation, the synthetic activity decreased sharply, indicating the predominant contribution of the damaging effect of irradiation, whereas under continuous irradiation, as a result of the stimulatory effect of low-dose irradiation, the synthetic activity increased during the first stage. Received: 11 May 1998 / Accepted in revised form: 10 January 1999     

Effect of gamma-radiation on the content of vitamin E in rats

The dynamics of vitamin E dose-dependence in the blood serum of Vistar line male rats after the total single irradiation with 60Co gamma-quantums in 0.2; 0.5; 1.0; 3.0 and 5.0 Gy doses (during 120 days); 7.0 Gy (during 20 days); 9.0 Gy (during 15 days) were studied. The vitamin E content values both in the norm and in 0.5, 1, 2, 4, 6, 8, 10, 15, 20, 30, 45, 65, 90 and 120 days after irradiation are given. The experiment data show that the dose dependence of vitamin E products has wavelike character. The possible causes of the vitamin E level decrease under intake of small and high doses of gamma-irradiation are discussed.     

Effects of gamma-irradiation on survival, growth and productivity of broiler chicken

In experiments with broiler chicken the influence of gamma-irradiation (137Cs) to survive and productivity of meat poultry was studied. LD50/30 increased from 10.0 to 18.7 Gy with increasing of the age of the irradiated chicken from 3 to 40 days and reduced from 18.3 to 11.9 Gy with increasing of a dose rate from 1.0 to 40.0 Gy/h. As a rule, death of chicken was observed between 4th and 15th days after the exposure; the most early dates of poultry death were found at irradiation dose rate of 40.0 Gy/h. The exposure to doses of 8-20 Gy resulted in stunted growth; in comparison with control group the mass reduced by 22-32 g per each 1 Gy, lowering of meat productivity by 36%.     

Fractionated, low-dose-rate ionizing radiation exposure and chronic ulcerative dermatitis in normal and Trp53 heterozygous C57BL/6 mice

The influence of low-dose-rate chronic radiation exposure and adaptive responses on non-cancer diseases is largely unknown. We examined the effect of low-dose/low-dose-rate fractionated or single exposures on spontaneous chronic ulcerative dermatitis in Trp53 normal or heterozygous female C57BL/6 mice. From 6 weeks of age, mice were exposed 5 days/week to single daily doses (0.33 mGy, 0.7 mGy/h) totaling 48, 97 or 146 mGy over 30, 60 or 90 weeks, and other Trp53+/- mice were exposed to a single dose of 10 mGy (0.5 mGy/min) at 20 weeks of age. The 90-week exposure produced an adaptive response, decreasing both disease frequency and severity in Trp53+/+ mice and extending the life span of older animals euthanized due to severe disease. The 30- or 60-week exposures had no significant protective or detrimental effect. In contrast, the chronic, fractionated exposure for 30 or 60 weeks significantly increased the frequency and severity of the disease in older Trp53+/- mice, significantly decreasing the life span of the animals required to be euthanized for disease. Similarly, the single 10-mGy exposure also increased disease frequency in older animals. However, the chronic, fractionated exposure for 90 weeks prevented these detrimental effects, with disease frequency and severity not different from unexposed controls. We conclude that very low-dose fractionated exposures can induce a protective adaptive response in both Trp53 normal and heterozygous mice, but that a lower threshold level of exposure, similar in both cases, must first be passed. In mice with reduced Trp53 functionality, doses below the threshold can produce detrimental effects.     

Characteristics of the development of interphase death of hematopoietic tissue in dogs in response to gamma irradiation

In experiments with 2-3 week dogs it was shown that whole-body gamma-irradiation with a dose of 3 Gy causes an insignificant absolute rise in the amount of degrading chromatin of the haemopoietic organs during the first 24 h following irradiation. After 48 h, this cell death parameter is normalized. A considerably lower radiosensitivity of lymphoid cells of dogs compared to small laboratory animals is indicated by a stable DNA content per 1 g of thymus, intactness of its structure after irradiation, and the absence of an increase in thymidine content of blood of young and adult dogs under the effect of 3-3.7 Gy radiation.