Restoration Effects of Glucose Refeeding on Reduced Synthesis of Albumin and Total Protein and on Disaggregated Polyribosomes in Liver of Starved Rats: Evidence of a Post-Transcriptional Control Mechanism

Abstract

Previous studies demonstrated that fasting is accompanied with a reduction of liver protein and albumin synthesis. A protein-deficient diet also leads to a marked change in liver RNA and protein metabolism. Although the reduction of protein synthesis and the disaggregated polyribosomes during fasting can be corrected by a single feeding of protein or a complete amino acid mixture, no or little changes of amino acid concentrations were found in portal blood and liver cytosol of fasted animals as compared to those of the fed group. To determine the effect of glucose on the reduced rate of protein and albumin synthesis of fasted rats, free and membrane-bound polyribosomes were isolated quantitatively from liver of starved rats (42-66 h) at different intervals after a single feeding of glucose and after giving glucose ad libitum for 24 h. (1) The yield of polyribosomal RNA decreased dramatically after a 42- to 66-hour starvation. A glucose refeeding did not change the RNA content. However, the restoration of polyribosome size could be observed rapidly. (2) At various levels of RNA, there was a decreased protein synthesis in fasted animals. However, the synthesis was enhanced after glucose refeeding. The albumin synthesis was also proportionately increased (10-12% of total protein synthesis of membrane-bound polyribosomes). (3) Glucose refeeding had no influence on the content of albumin mRNA sequence and liver RNA. These findings suggest that the effect of glucose on the restoration of protein and albumin synthesis is a sole post-transcriptional event.