Early and Late Effects of Tritiated Thymidine upon the Replication of Splenic Lymphocytes

Studies were made of the early and late effects of3 H- TdR labeling of DNA upon the replication of spleen lymphocytes in 3-week-old Wistar strain rats. The administration of 1 μCi/g body wt was associated with an asymmetrical mitotic labeling curve in which the first cycle was fairly well defined but the subsequent two cycles were less so. After 0.4 μCi/g, two cycles were observed of similar duration to those after 1 μCi. Following 2 and 10 μCi/g the pattern was disrupted. The effects were greater with the higher labeling dose and were related to the level of radiation and not to that of thymidine pool dilution. Five weeks after 2 and 10 μCi/g, when autoradiographic evidence of retained radioactive labeling was absent, the cycle patterns were still altered. Four months after 10 μCi/g the pattern was restored to that of age controls. The differences between the responses of spleen lymphocytes, on the one hand, and of previously studied coexistent hepatocytes and ileal cells, on the other, are reviewed.