TRANSLATIONAL REGULATION OF PROTEIN-SYNTHESIS IN THE LIVER AND SKELETAL-MUSCLE OF MICE IN RESPONSE TO REFEEDING

To identify the mechanism that modulates the rate of protein synthesis in different tissues responding to food intake, several parameters of translational activities were measured together with the rate of protein synthesis in the liver and skeletal muscle. In 18-hour fasted mice, protein synthesis in muscle and the liver was stimulated by refeeding a complete diet after I hour. Refeeding a protein-free diet increased the protein synthesis in the liver but not in muscle. Injection of anti-insulin serum suppressed the response to refeeding in both tissues except to a complete diet in the liver. The response of liver protein synthesis to food intake is not necessarily mediated by insulin, provided an abrupt, large increase in plasma amino acid concentration occurs. In contrast to the liver, an elevation of insulin level is essential for the stimulation of protein synthesis in muscle along with a high concentration of plasma amino acids. The stimulation of elongation activity in addition to stimulation of the initiation activity contributed to the enhancement of protein synthesis induced by refeeding in both the liver and muscle. In another set of experiments, we also observed a delayed rise of elongation coupled with an immediate rise of initiation in the liver after refeeding.