Insulin effects on protein synthesis are independent of glucose and energy metabolism

Protein synthesis was accelerated in rat hearts that were provided insulin compared with provision of glucose or pyruvate alone or a mixture of glucose and pyruvate. The faster synthetic rates were accompanied by a reduction in numbers of ribosomal subunits, indicating that peptide chain initiation was accelerated relative to elongation/termination. In hearts supplied glucose, 65% of the maximal effect on protein sythesis was achieved by addition of 1.7 x 10^-10 M insulin, but significant effects on glucose uptake as well as on tissue contents of glucose 6-phosphate and creatine phosphate were obtained only with 7 x 10^-10 M insulin. Addition of glucose to perfusates containing pyruvate did not accelerate protein synthesis, although the glucose 6-phosphate content was raised. Similarly, the stimulatory effects of insulin on protein synthesis in hearts supplied pyruvate did not depend on changes in glucose 6-phosphate content, creatine phosphate/creatine, ATP/ADP, or adenylate energy charge. These studies indicate that insulin accelerated peptide-chain initiation and protein synthesis in rat heart by mechanisms independent of the hormone's effect on glucose or energy metabolism.