Abstract

We have investigated certain events occurring in rat liver cytoplasm during the time period between the administration of hydrocortisone and the hormone-induced increase in the level of several hepatic enzymes. At various times after the administration of hydrocortisone to adrenalectomized rats, ¹⁴C-orotic acid was injected intraperitoneally. After a 40-min labeling period the rats were killed and liver cytoplasm was examined on sucrose gradients. Two hours post hydrocortisone administration the isotopic labeling of a 45 S cytoplasmic particle was markedly increased. Previous data suggest that the 45 S particle carries newly synthesized messenger RNA from the nucleus to the cytoplasmic polyribosomes. The stimulation of labeling occurred at a time consistent with the postulate that the excess of labeled RNA in the 45 S particle includes messenger RNA coding for the synthesis of the hormone-stimulated enzymes. A simultaneous fall in membrane-free, monomeric ribosomes was noted.