Ultradian Rhythms of Tumor Resistance System Activity

Abstract

Ultradian time-dependency of the carcinogenic effect was studied in mice; both the model of transplanted (leukemia EL-4) and that of chemically-induced (urethane-induced lung adenomas) tumor were used. As the possible mechanisms which are attributable to this phenomenon, ultradian variations in cellularity of the lymphoid organs (thymus, lymph nodes, spleen, bone marrow), in natural killer-cell (NK) activity, level of the serum factors modifying lymphocyte migration, and in activity of the liver carcinogen-metabolizing enzyme system were investigated. All these characteristics were determined hourly in intact mice. Both the life span of mice inoculated with tumor cells, and the yield of carcinogen-induced tumors were found to be ultradian dependent (periods 3-8 hr). Ultradian dependency was found also for the number of lymphocytes in the lymphoid organs, the number of karyocytes in bone marrow, the NK activity against tumor cells, the migration index of normal spleen cells in the presence of tumor cells, as well as for the activity of the carcinogen-metabolizing enzyme system. It is suggested that variations in the natural resistance against transplanted or chemically-induced tumors may be due to the variations in these parameters.