Changes in liver polyribosome patterns following administration of hydrocortisone and actinomycin D

Abstract

1. The postmitochondrial supernatant fraction was prepared from the livers of fasting adrenalectomized rats. Part was used without detergent treatment to provide a mixture of free ribosome aggregates and microsomes. Another portion was treated with deoxycholate to yield the total population of ribosomes from both free and membrane-attached sources. These two postmitochondrial preparations were resolved into monosomes, disomes and polysomes on sucrose density gradients either directly or after passage through 2 M sucrose on a zonal gradient. Passage of the ribosome populations through the zonal gradient resulted in a selective loss of a large part of the monosomes and some disomes. In consequence, this type of profile was less sensitive to different treatments, and was not used to study the action of hydrocortisone and of actinomycin on liver ribosome populations. 2. The total ribosome population of the liver showed a loss of polysomes following treatment of animals with actinomycin. At the same time, disomes accumulated in the free ribosome fraction of the liver. 3. Administration of hydrocortisone phosphate was followed a few hours later by diminution of the monosome-disome component of the total ribosome population, and a corresponding accumulation of polysomes. Simultaneous or previous injection of actinomycin D did not prevent the hormone from having this action. It has been concluded that corticosteroid hormones can cause aggregation of liver ribosomes through mechanisms not requiring synthesis of additional RNA.