EFFECT OF INSULIN IN THE PRESENCE OF GLUCOSE AND AFTER DEPLETION OF GLUCOSE, GLUCOSE 6-PHOSPHATE AND GLYCOGEN By ERNST B. CHAIN and PETER M. SENDER*

In the absence of glucose, insulin stimulated the incorporation of 14C-labelled amino acids into protein by perfused rat hearts that had been previously substantially depleted of endogenous glucose, glucose 6-phosphate and glycogen by substrate-free perfusion. This stimulation was also demonstrated in hearts perfused with buffer containing 2-deoxy-D-glucose, an inhibitor of glucose utilization. It is concluded that insulin exerts an effect on protein synthesis independent of its action on glucose metabolism. Streptozotocin-induced diabetes was found to have no effect either on 14C-labelled amino acid incorporation by the perfused heart or on the polyribosome profile and amino acidincorporating activity of polyribosomes prepared from the non-perfused hearts of these insulin-deficient rats, which show marked abnormalities in glucose metabolism. Protein synthesis was not diminished in the perfused hearts from rats treated with anti-insulin antiserum. The significance of these findings is discussed in relation to the reported effects of insulin deficiency on protein synthesis in skeletal muscle.