Influence of Early and Prolonged Protein Depletion in the Diet on in vitro Protein Synthesis in Muscle and Liver of Rats

Abstract

Abstract Male rats weighing about 200 g were killed after 1, 2, 4, 10, and 20 days on a protein-free diet, and in vitro synthesis of protein was measured by the incorporation of 14C-glycine into protein of liver slices and isolated soleus muscle. The incorporation value was corrected for the differences in specific radioactivity of intracellular free glycine, and protein and RNA contents of tissue were determined. Muscle protein synthesis began to decrease from the 1st day of depletion, fell rapidly until the 4th day, and then was reduced gradually to about 30 % of the initial control by the 20th day. This reduction was due in a major part to a fall in the rate of protein synthesis per unit of RNA and in a minor part to a decline in RNA content. In the liver, protein synthesis increased in the early period of protein depletion, but declined with prolonged depletion, and was reduced greatly by severe depletion. These alterations were caused mainly by the changes in incorporative activity per unit of RNA. From these results, it was suggested that different patterns of adaptive response to protein depletion occurred in both cases of early and prolonged depletion in connection with protein metabolism in rats.