Effect of Diet on Protein Synthesis and Nucleic Acid Levels in Rat Liver

Abstract

The effects of variation in dietary protein content on the rates of liver protein and plasma albumin synthesis have been reinvestigated. Adult rats were preconditioned to normal (27%), high (64%), low (8%) and protein-free diets for 5 to 7 weeks. Following a 4-hour fast they were injected with DL-lysine-1-14C intravenously at different time intervals up to 2 hours before killing. Determinations were made of DNA, RNA, protein, and free lysine concentrations in the liver, and of the specific activity of lysine in the protein-bound and TCA-soluble fractions. The rate of liver protein synthesis remained relatively unchanged in low and high protein diet groups, as compared with the normal protein diet group, and was either unchanged or slightly increased in the animals on the protein-free diet. On the other hand, the rate of plasma albumin synthesis was significantly reduced in protein deprivation, although it did not show any appreciable differences among other groups. DNA, content was found to be higher in the liver of rats fed the protein-free diet, as compared with those on normal diet, whereas RNA concentration was reduced considerably, the differences among other groups being small. Protein content of the liver changed proportionate to the protein content of the diet. Free lysine concentration in the liver was found to be relatively unaffected by dietary treatment.