The effect of actinomycin D on stem hemopoietic cells in the bone marrow of adult mice has been studied by means of spleen colonies. The antibiotic at a dose of 0.4 mu g/ml (g) inhibited the colony formation when applied in vitro and stimulated this process in vivo. The reaction of stem hemopoietic cells to the antibiotic at a dose 0.04 mu g/ml (g) varied: in most experiments no cytotoxic effect was observed both in vitro and in vivo; moreover, in some cases the colony formation increased 1.5--2 times. Possible causes of the stimulating and inhibiting effect of the antibiotic are discussed.

Simultaneous administration to B6 female mice of deoxycytidine in doses exceeding 2--3-fold those of cytosar (20 mg/kg three times a day for 4 days) prevents lethal toxicity induced by cytosar, protects the bone marrow and spleen, hemopoietic stem cells, myeloid and erythroid cells of the bone marrow, spleen and blood. It also protects spleen and blood lymphocytes from cytosar toxic effect by does not protect thymus or bone marrow lymphocytes.

The distribution of donor cells in the connective tissue of different organs of xenogeneic (rat in mouse) radiation chimaeras was studied under the normal conditions and upon its de novo formation. The donor cells were identified by means of indirect immunofluorescent method with the use of specific antiserum against surface antigens of the rat bone marrow cells. It was shown that macrophages of subcutaneous connective tissue, lung alveolar macrophages, Kuppfer's cells, macrophages of intestinal mucosa in the long living radiochimaeras were represented by the donor cells. The fibroblast-like cells of donor origin were found in the subcutaneous loose connective tissue, among the connective tissue elements of cross striated muscles, in the cardiac muscle, in the intestinal mucosa. The repopulation of Peyer's patches of the radiochimaeras by the donor cells was demonstrated. The macrophages of hemopoietic origin (donor origin) were found in the inflammatory granuloma in the brain cortex. The donor cells were found in the connective tissue of mammary glands following the hormonal stimulation. Differences were found with respect to binding of the antiserum used to cells of the capsule around the foreign body in different organs of xenogeneic chimaeras.

The activated mouse T-cells release in the culture medium a factor suppressing the ability of stem hemopoietic cells to form hemopoietic colonies in the spleens of lethally irradiated recipients. The factor of stem cell inhibition (FISC) obtained from the mouse thymocytes on the 1st, 7th and 10th day of postnatal life does not differ, by its inhibiting activity, from that obtained from the adult thymocytes, whereas the embryonic thymocytes under similar experimental conditions released FISC with a low inhibiting activity. A study of some physical-chemical and biological properties of FISC has shown that the latter is actively synthesized both by cortical and medullary thymocytes, has no (linear) specificity and resembles, by its characteristics, lymphokins of a wide effect, such as MIF and LT, rather than short-distant mediators, such as suppressor and helper factors.

The aspects of structure and function of the APUD-system under normal and pathological conditions are analysed. New terms and concepts (apudocyte, apudoblast, apudogenesis, apudopathies) applicable to the APUD-system are introduced. It is suggested that some apudocytes originate from polypotential stem cells. The dysfunctions of the APUD-system (apudopathies) are described, their classification is suggested, and the role of apudocytes in the endogenous mechanisms of oncogenesis is analysed.

Experiments on rats given weekly injections of the intestinal carcinogen 1,2-dimethylhydrazine (DMH) have shown that liver and colon DNA accumulated 7-methylguanine and some methylated adducts of adenine. In addition, DNA of liver tissues and crypt bottom cells accumulated O6-methylguanine. The conclusion is drawn on the role of its persistence in DNA of stem enterocytes in the initiation of colonic carcinogenesis. The mechanism of liver tissue resistance to the carcinogenic effect of DMH is discussed.

A study was made of the duration of early developmental stages in F1CBA/C57BL mouse hybrid embryos. It was found that the longest were zygota and 2-cell stages. During cleavage the developmental stages became about 2 times shorter. The 4-cell stage was the shortest. The duration of the cleavage stages in the test mouse embryos was different from that in mouse embryos of other strains reported in the literature. These findings suggest that the genetic features of mice belonging to different strains exert an effect on the duration of cleavage stages.