[Effect of various concentrations of 3H-thymidine on the kinetics of Chinese hamster cell division].

A study of the asynchronous culture of Chinese hamster fibroblasts by autoradiography has shown that the pulse (15 min) incorporation of 3H-thymidine in nuclear DNA influences the kinetics of labeled cell proliferation. The results obtained suggest that one of the early biological effects of the pulse incorporation of 3H-thymidine is a delay in the occurrence of the first mitosis. With the concentration of 3H-thymidine 37 kBq/ml the slowing down of of the movement of labeled cells in the cycle is detected by a shift and overlapping of waves of labeled and unlabeled mitotic cells. In an increase of the concentration up to 370-925 kBq/ml the pattern of the curves of labeled mitotic cells is distorted. These distortions are well interpreted by the nature of change of the index of labeled and unlabeled mitotic cells. A lowered index of labeled nuclei points to a decrease in the proliferative activity of labeled cells. After an increase in 3H-thymidine concentration from 37 up to 370-925 kBq/ml the mitotic activity of cells labeled at the end of S-phase decreases from 1 to 0.6-0.1% respectively. With the concentration of 925 kBq/ml for these cells incorporating 3H-thymidine at the end of S-phase, a delay of the entry into mitosis reaches 6-8 h. Autoradiography data with the assessment of granule density suggest that mitotic activity and the period of delay in the occurrence of mitosis depend on the dose of irradiation with intranuclear tritium. Thus the tritium dose rate after 15 min of incubation with 3H-thymidine is 0.03, 0.27 and 0.69 Gy/h for concentrations 37,370 and 925 kBq/ml respectively.