Effects of Adrenal Hormones upon DNA Synthesis in Regenerating Rat Liver and Tumors*

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Abstract
1. When rats were pretreated with cortisone (5mg. daily for 5 days prior to partial hepatectomy), the increase in the DNA synthesis which would usually occur during the course of liver regeneration was greatly retarded, the induction of thymidine kinase [EC 2.7.1.21] and thymidylate kinase(s) [EC 2.7.4.9] being also retarded by the same treatment. 2. The injections of adrenalin (15–25μg. hourly) was also found to be effective in inhibiting the DNA synthesis and thymidine kinase induction occuring in regenerating livers, although no such effects were produced in the case of hepatoma cells. 3. The effect of adrenalin was found to be the greatest when administered during an early period of regeneration, during which time the induction mechanism would still be operating, this effect becoming smaller when it was given later than 24 hours after partial hepatectomy. 4. Suggestions were put forward that the action of adrenalin might be more direct than that of cortisone and that it might be acting somewhere at a stage preceding the S phase, probably at “dicho-phase” of mitosis cycle. The possible mode of action of cortisone was also discussed in relation to the behavior of lymphocytes.

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