Tryptophan-mediated induction of hepatic enzymes stimulated by 5-azacytidine pretreatment.

The effect of 5-azacytidine on tryptophan-mediated induction of various enzymes in rat livers was analyzed. Pretreatment of animals with 5-azacytidine results in a different response of tryptophan oxygenase to tryptophan and cortisone administration. While the hormonal induction of this enzyme was not affected by the drug, the tryptophan-mediated induction was stimulated. Pretreatment of rats with 5-azacytidine resulted also in the enhancement of liver tyrosine aminotransferase activity. There was no difference between the effect of tryptophan and cortisone. Tryptophan affects also the level of thymidine kinase at various stages of liver regeneration. 5-azacytidine given 16-40 hours prior to partial hepatectomy resulted in the enhancement of thymidine kinase activity at 24 hours of regeneration.