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 prot ein synthesis in the liver and skeletal muscle. In 18-hour fasted mice , protein synthesis in muscle and the liver was stimulated by refeedin g a complete diet after I hour. Refeeding a protein-free diet increase d the protein synthesis in the liver but not in muscle. Injection of a nti-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, prov ided an abrupt, large increase in plasma amino acid concentration occu rs. In contrast to the liver, an elevation of insulin level is essenti al for the stimulation of protein synthesis in muscle along with a hig h concentration of plasma amino acids. The stimulation of elongation a ctivity in addition to stimulation of the initiation activity contribu ted to the enhancement of protein synthesis induced by refeeding in bo th the liver and muscle. In another set of experiments, we also observ ed a delayed rise of elongation coupled with an immediate rise of init iation in the liver after refeeding.