Cytogenetic changes in the bone marrow cells of long-term irradiated rats]

The occurrence and characteristics of the chromosome structural changes in femur bone marrow cells under continuous irradiation with the exposure rate of 50 R/day within 90 days was followed. The 25% increase in the chromosome aberration frequency was observed within 7 days of the irradiation, and then the aberration rate was constant up to the end of the irradiation (90 days).     

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.     

Effect of radioprotective agents on the epithelium of small intestine mucosa in irradiated animals

In experiments on irradiated (10 Gy) mice a study was made of the morphological changes in the small intestine mucosa and in its functional status estimated by absorption of stain uranine. It was shown that the preventive administration of cystamine and S-(omega)-aminopropyl-beta-aminoethylthiophosphoric acid to the exposed mice increased the proliferation processes in the crypt and the cell movement per villus providing a favourable effect of the radioprotective agents on the absorption function.     

Rubidium transport in irradiated vitamin-E-deficient bone marrow cells

We showed previously that the Rb⁺ transport rate in bone marrow cells (BMC) of vitamin-E-deficient mice is significantly lower than that in BMC of euvitaminotic mice. It is now evident that 4 h after whole-body, low-dose (0.01–1.0 Gy) gamma-irradiation of avitaminotic mice, there is an increase in the rate of Rb⁺ transport. This increase is quite pronounced, exceeding at all dose levels the rate of Rb⁺ transport in euvitaminotic mice exposed to the same radiation dose.On leave from the University of Rochester, School of Medicine and Dentistry, Department of Biophysics, Rochester, New York, USA     

Postovariectomy bone marrow changes in irradiated and unirradiated wistar rats

Bilateral ovariectomy of Wistar rats has per se a stimulative effect on the myeloid tissue, determining a hypercellularity of this organ-tissue. On the other hand, under the conditions of a whole-body irradiation with a single dose of 800 r X-rays, bilateral ovariectomy manifests a protective effect on the myeloid tissue preventing the development of hypoplastic, respectively aplastic modifications.     

The formation and repair of DNA breaks in subpopulations of irradiated rat bone marrow cells

Using the method of viscosimetry of alkaline lysates it was shown that the saturable DNA repair system was present in rat bone marrow cells which was described by a complex kinetics. Isokinetic fractionation in a sucrose and dextran gradient permitted to isolate three fractions differing in the ratio between differentiated cells and cells capable of division. The estimation of the postirradiation DNA repair kinetics in these cells revealed a comparatively high level of repair in normocytes which confirmed the presence of the relationship between the level of DNA repair in cells and their proliferative potency.     

Electrophoretic analysis of the internucleosome fragmentation of DNA in irradiated thymocytes of rats

Total DNA and DNA of chromatin degradation products obtained from rat thymocytes 6 h after irradiation with a dose of 10 Gy were separated electrophoretically. Relative shares of mononucleosomes and their oligomers were determined. Experimental distributions of DNA fragments differ from those calculated on the basis of the assumption of a random breakage of bonds between the nucleosomes.     

Structural characteristics of the mucosa of the small intestine in gnotobiote rats]

Histological and electron microscopic investigations of mucosal strucutre of the small intestine in gnotobiotic and conventional rats have demonstrated that mucosal index (lenear dimentions of villi/crypt dimentions ratio) is equal to 3--4 and 1.4--2.5, respectively. In gnotobiotic rats the number of mitotic figures in crypts is less, migratory-desquamative parameters of enterocytes are 5--6 days, cranio-caudal gradient of linear dimentions of villi, crypts and the number of goblet-shaped cells is not expressed. The goblet-shaped cells and cells with acidophilic granules have secretion of moderate intensity. The number of cells infiltrating epithelium of villi and crypts is greater when microbes are present in the gut lumen. A considerable difference in the structure of the connective tissue basis of the gnotobiotic and conventional rats mucosa are also connected with presence or absence of microflora in the gut lumen.     

Cloning stem cells in the bone marrow of irradiated mice]

Different amount of intact or irradiated bone marrow from syngenous donors was administered to mice irradiated with a lethal dose. There was revealed a linear dependence of the number of the 8-9-day colonies grown in the bone marrow of the femur on the amount of the administered cells, and an exponential dependence on the irradiation dose. Regularity of the stem cell cloning in the bone marrow was analogous to such in the spleen. Radiosensitivity of the colony-forming units (CFU) differed depending on the site (the spleen, the bone marrow) of their colony formation. The CFU settling in the marrow proved to be more radioresistant (D(0) equalled 160-200 P) in comparison with the CFU settling in the spleen (D(0) constituted 80-100 P). It is supposed that a different radiosensitivity of the CFU was caused by the presence of heterogenic population of the stem cells and also by specific peculiarities of the organ (the spleen, the bone marrow) in which the colonies formed.     

The inhibition by the tumor necrosis factor of the death and DNA fragmentation of lymphoid cells in irradiated rats]

The influence of a tumor necrosis factor, administered 16 h before irradiation of rats, on the radiation response of thymus and bone marrow cells has been investigated. Three and 6 h after irradiation the following indices were analyzed: the number of apoptotic cells in the thymus; the accumulation of polydeoxyribonucleotides and the appearance of single-strand breaks in DNA of bone marrow and thymus cells; and the electrophoretic properties of thymocyte DNA. The injection of a tumor necrosis factor reduced the number of polydeoxyribonucleotides, inhibited internucleosome DNA fragmentation, and did not influence the formation of single-strand breaks in DNA.     

Degree of chromatin fragmentation and frequency of nuclear pyknosis in Percoll-fractionated thymocytes of irradiated rats

The relationship between nuclear chromatin degradation to polydeoxyribonucleotides (PDN) and other features of interphase death were studied using thymocytes of normal and X-irradiated rats. Fractionation of the thymic cells in Percoll gradients was performed in order to separate dead from intact cells. The degree of radiation-induced chromatin fragmentation, as assessed by electrophoresis, was similar for PDN from all Percoll bands. Following irradiation 87-98 per cent of 'heavy' thymocytes were pyknotic and almost devoid of receptors to autologous erythrocytes thus comprising a dead cell population. A direct relationship between PDN content and nuclear pyknosis was noted throughout the gradient. The loss of autologous rosette-forming ability was directly related to other indices of interphase death. The possibility of PDN originating from pyknosis-prone cells and the capacity of radiosensitive thymocytes to form autologous rosettes are discussed.