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Nucleic Acid Metabolism in Regenerating Rat Liver

VII. Effect of X-Radiation on Enzymes of DNA Synthesis^*

F. J. Bollum, J. W. Anderegg, Anne B. McElya and Van R. Potter

( McArdle Memorial Laboratory, University of Wisconsin, Madison 6, Wis.)

The effect of x-radiation on the appearance of thymidine kinase and DNA poly merase in regenerating rat liver was studied as a function of dose (375,750, and 1500 r) and time of administration of radiation (6 or 16 hours) relative to the time of partial hepatectomy.

When the radiation was given 6 hours after operation, all levels of radiation produced essentially complete inhibition of the increase in enzyme levels that would be expected to occur between 6 and 24 hours after partial hepatectomy.

When the radiation was given 16 hours after operation, a time previously shown to completely block DNA synthesis in regenerating liver in vivo, the usual increase between 16 and 24 hours was not prevented.

The results are discussed in relation to data obtained on whole animals, and it is suggested that inhibition observed in in vivo studies with radiation given 16 hours after operation must be explained in terms other than the inhibition of thymidine kinase or DNA polymerase or their formation, while radiation given 6 hours after operation may act by preventing the formation of the appropriate enzyme-forming systems.

^* Supported in part by a grant (C-646) from the National Cancer Institute, National Institutes of Health, U.S. Public Health Service.

Postdoctoral Fellow, U.S. Public Health Service, 1956–1958.

Present address: Biology Division, Oak Ridge National Laboratory, Oak Ridge, Tenn.

Present address: Depts. of Zoology and Physics, University of Wisconsin, Madison, Wis.

Received 8/10/59.