A non-invasive micronucleus assay in the rat liver

The potent rat-liver mitogen 4-acetylaminofluorene (4AAF) is shown here to provide an effective replacement for the surgical procedure of 2/3 partial hepatectomy (2/3PH) in the in vivo rat-liver micronucleus assay described by Tates and his colleagues. This protocol modification enables the assay to be conducted on a routine basis. Control observations for both 2/3PH and 4AAF-treated rats are presented, together with evidence indicating 4AAF itself to be without activity in the assay, irrespective of the mitogenic stimulus. The activities of the rat carcinogens DMN, 2AAF, DMH and 6BT, and of the non-carcinogens 4AAF and 4N are demonstrated. Recommendations for the conduct of the modified assay are made.     

Thermally Enhanced Radiosensitivity of Cultured Chinese Hamster Cells

X-IRRADIATION of mammalian cells in culture yields a survival curve of the threshold type (for review see ref. 1). It isjnter-esting to ask how one can enhance the radiation response by small changes of the physical environment of the cells, as can be done chemically, for example, by incorporation of 5-bromo-deoxyuridine into DNA^1,2. Elevation of the temperature is a likely prospect for enhancement of radiosensitivity for the following reasons. It is known that proteins are heat labile and that temperature sensitive mutants of bacteria and phage can be obtained for many different enzymes³ which are operative at 37° C but not at 42° or 43°C. For example⁴, DNA polymerase is reversibly temperature sensitive; it is rendered inoperative above 42°C, but will be functional again when the temperature is lowered. It is not unreasonable to expect that temperature sensitive mutations for many enzymes occur frequently and that the use of temperatures somewhat higher than the normal range at which the cells grow might disclose sensitivities for specific enzymes in normal cells of higher organisms.     

Interferon inhibits DNA Synthesis induced in Mouse Lymphocyte Suspensions by Phytohaemagglutinin or by Allogeneic Cells

IN addition to its well known antiviral activity, interferon has recently been shown to inhibit the multiplication of tumour and mammalian cells in cell culture^1–6. We report here the inhibition by interferon of DNA synthesis induced in mouse spleen lymphocytes by the non-viral stimuli phytohaemagglutinin (PHA) and allogeneic lymphocytes. These findings are in accord with our contention that interferon affects cell function and, furthermore, they suggest that by acting on lymphocytes, interferon plays a role in the immunological response of the host.