A Biochemical and Autoradiographic Study of the in Vivo Utilization of Tritiated Thymidine in Regenerating Rat Liver1

erating rat liver under specific experimental conditions has been evaluated by autora diographic and biochemical methods. A rapid disappearance of the labeled thymidine from the blood in the 1st 10 mm was accompanied by a rapid incorporation of the radio activity into the acid-soluble fraction and DNA of the liver cells. Two mm after ad ministration, label was found in T?tIP, TDP, TTP, and DNA. A relatively constant ratio of these labeled precursor components in ASF during the 1st hr after injection suggests that equilibrium was reached immediately after administration. The predominant biologic action in liver following administration is the rapid de struction of thymidine. Only 2 mm after injection, @ of the labeled thymidine in the ASF of the liver cells had been degraded to T and BAIB. This marked destruction is also shown by the fact that only 1.2 % of the injected thymidine is incorporated into newly formed DNA. All the thymidine is removed from the blood within 1 hr. The results indicate that, under the specific experimental conditions, TdR-3H can be used as an index for DNA synthesis in individual cells as well as in the total cell population within 1 hr after administration.