The effect of streptozotocin diabetes on brain protein synthesis in the rat

Young normal control rats were compared with a group made diabetic by treatment with streptozotocin and with other normal rats maintained on a restricted diet to obtain a daily body weight change similar to that of the diabetics. In diabetic rats plasma levels of Val, Ile and Leu rose and those of Asp, Thr, Ser, Gln, Gly, Tyr, Orn, Lys, His and Arg decreased, whereas brain concentrations of Leu, Arg and Orn were augmented and those of Thr and Ser reduced. Insulin treatment diminished these differences in comparison with controls values. In food-restricted normal rats plasma and brain amino acid concentrations also differed from values in normal controls but they were of different magnitude and/or direction than those of diabetics. In vitro 3H-Leucine incorporation into proteins by brain postmitochondrial dialyzed supernatants was unaffected in both diabetic and food-restricted rats, whereas in liver preparations the same parameter was significantly reduced in both groups and insulin treatment of the diabetics decreased this difference. Results indicate that brain amino acid concentrations in diabetic animals are a secondary consequence of their circulating levels and of potential modifications of brain amino acid metabolism other than protein synthesis, which is unaffected.