E.H. Betz

Variations of liver cell control during diethylnitrosamine carcinogenesis

Abstract Male Wistar rats chronically treated with diethylnitrosamine (DENA) ( 80 mg/l in drinking water) develop liver carcinomas mostly after the 90 th day of treatment. Experiments were planned in order to investigate the cell kinetics of liver during the preneoplastic period (up to the 60 th day). The mitotic response of the liver was studied in various conditions: in animals treated with DENA alone and in DENA treated rats submitted to a partial hepatectomy. Furthermore, normal hepatectomized rats were treated with liver extracts obtained in various conditions (normal and DENA treated rats). The extracts were prepared in order to purify mitotic inhibiting substances (chalone activity) normally present in liver tissue. During the two first weeks of treatment, DENA induces a transient increase of mitotic index; after partial hepatectomy, the mitotic response is approximately normal. The cell divisions present during this period a normal circadian rhythm. After the 30 th day of treatment, the mitotic index decreases significantly, the response to the partial hepatectomy is reduced and the circadian rhythm of divisions is lost. During this period, glycogen retaining areas develop in the liver; no difference is observed between the response of these areas and that of adjacent parenchyma. An extract obtained from a normal liver inhibits to a large extent the 3 H-thymidine DNA label and the mitotic response induced by a partial hepatectomy. A similar extract obtained from the liver tissue taken 24 hr after hepatectomy has no inhibitory effect. Extracts from liver of rats treated during 30 and 60 days with DENA behave in the same way as an extract from regenerating liver and produce no inhibition. The results indicate that the preneoplastic period shows at least two successive phases. During the two first weeks, the mechanisms controlling the cell homeostasis of liver tissue seem to function normally. Later on, there seems to be an important disturbance of these mechanisms.

Liver cell control after discontinuation of DENA feeding in hepatocarcinogenesis

Abstract The mitotic response following a partial hepatectomy, the nyctohemeral rhythm of these mitoses and the ‘chalone activity’ measured by the inhibitory effect of liver extracts on the normal liver regeneration have been studied in order to estimate the evolution of mitotic control in the liver of rats treated by DENA for 2, 4, 6 and 10 weeks. These parameters and the pathological lesions (preneoplastic foci, neoplastic nodules and hepatomas) have been followed up after stopping the DENA feeding. A good correlation has been found between the malignant transformation of preneoplastic foci and the breakdown of the mitotic control. In animals treated by DENA for two weeks, the homeostatic control of mitoses remains normal for a minimum of 14 months and ‘preneoplastic foci’ persist without any further malignant transformation. After DENA feeding for 4 and 6 weeks, the subsequent malignant transformation occurs as a function of the mitotic disturbance: the longer the DENA feeding, the faster the homeostatic disturbance, the earlier the conceration. After DENA treatment for 10 weeks, the homeostatic regulation is lost and the neoplastic growth is triggered at the time of the DENA feeding cessation. In this case, the pattern of canceration is the same as when DENA is given continuously up to the time of death. It is concluded that ‘preneoplastic foci’ induced during the first two weeks of treatment cannot by themselves transform into a malignant tumor. To commit them irreversibly into malignancy, a subsequent action of the carcinogen is necessary; it may consist of the irreversible breakdown of the normal homostatic regulatory mechanism of liver cell proliferation.

Evidence of a G1regulation of circadian proliferation in mouse methylcholanthrene-induced sarcomas

Abstract In two methylcholanthrene induced sarcomas of C 57 BL male mice presenting a circadian proliferation (peak of mitoses at noon and peak of labelling indices between midnight and 4 a.m.), the authors performed per cent labelled mitosis curves every 6th hr during the 8th diurnal period of growth. The G 1 phase showed the most important variation with a significant increase in the groups receiving 3 H -thymidine at 2 a.m. The possibility that this periodic variation of G 1 phase regulates the circadian rhythm of cell proliferation is discussed.

Origin, morphologic and functional characteristics of a new lymphoid cell type in irradiated mouse bone marrow.

After sublethal irradiation, an immature lymphoid cell type with characteristic ultrastructure was found in the bone marrow and thymus of adult mice of different strains. Normally this cell type has only been detected in the embryo or new-born. Grafting normal, adult bone marrow suppresses, while thymectomy enhances the proliferation of these cells in the irradiated organism. Immunologic and functional tests suggest that the cells have either an embryonic origin, or are derivatives of haemopoietic stem cells and function either as precursors for the immunocompetent B and T cells, or in an entirely different lymphoid system.

Ultrastructural characterization of a thymic x-cell type in sublethally irradiated mouse. Correlations with the bone marrow X-cell population

Summary The ultrastructural study of the mouse thymus during recovery after a sublethal irradiation reveals the appearance in the subcapsular zone of a peculiar type of lymphoid blast cells, i.e. the “X-cells”. These peculiar cells are similar to those described in the bone marrow during the postirradiation lymphoid rebound. A normal syngeneic bone marrow graft after irradiation prevents the X-cell accumulation both in the thymus and the bone marrow. Several arguments suggest that X-cells do not participate actually in the thymic regeneration. It is postulated that thymic X-cells, like marrow X-cells, belong to an embryonic cell line reappearing in the adult mouse after irradiation. Chronological and topographical correlations with the thymic “immature lymphoid cells” suggest that the X-cell could be the target cell for the leukemogenic virus.

Influence of a mixture of chemical protectors on the lymphoid regeneration of bone marrow and thymus in irradiated mice.

In mouse, the administration of chemical protectors before an irradiation induces a more rapid bone marrow regeneration and an increased lymphoid rebound. In the thymus the late atrophy is reduced. Separately administrated, the protectors decrease greatly the thymocytes number but have no effect on the marrow population.

Ultrastructural autoradiographic study of blast cells in the mouse thymus. Interest for radioleukemia research.

Ultrastructural autoradiographic studies of mouse thymic blast cells after H3 Tdr injection show that their fine nuclear structure is related to their position in the cell cycle. The variations in the composition of the subcapsular blast cell population during radiation-induced leukemogenesis indicate kinetic changes in thymic lymphopoiesis, which are probably due to the oncogenic process.