Temporal Changes in DNA and RNA Synthesis in the Regenerating Liver of Hydrocortisone-treated Rats

Abstract

The initial rise in DNA synthesis in the regenerating liver of young adult rats is reversibly inhibited by the administration of hydrocortisone, 50 mg/kg, at the beginning of the S phase, i.e. , 19 hr after partial hepatectomy. DNA synthesis is reinitiated approximately 31 hr postoperatively in the regenerating liver of the hydrocortisone-treated rat, with peak synthesis then occurring 36 hr after partial hepatectomy, compared to after 26 hr in the controls. Despite the inhibition of DNA synthesis, the rate of ribosome formation is increased 150 to 200% at 26 hr in the hydrocortisone-treated rats; similarly, following release of DNA synthesis at 36 hr ribosome formation is elevated 120 to 200% over controls. An analysis of the rates of synthesis and processing of the rRNA in the nucleus and of the accumulation of the products in the cytoplasm suggests that most of the increase in the hydrocortisone-treated rats is due to increased transport of the ribosomal subunits to the cytoplasm.