Specificity of Tritiated Thymidine as a Precursor of DNA Under Conditions of Prolonged Administration 1

Summary

After 90 injections of thymidine-methyl-³H into adult mice at intervals of 8 hr, the radioactivities of several biochemical fractions (acid-soluble material, lipids, RNA, DNA, and protein) were determined in homogenates of various organs. A high specificity of incorporation of labeled thymidine into DNA was observed in tissues characterized by a high rate of cell proliferation, while this specificity was of a lower degree in tissues exhibiting a low rate of cell proliferation.

With few exceptions, the amounts of radioactivity (per gram wet weight) in the fractions other than DNA were similar for all organs tested. Approximately 70% of label contained in the acid-soluble fraction were in tritiated water, whereas no free thymidine-³H could be detected 1 hr after the last injection of this precursor.