Phenobarbitone-induced stimulation of protein synthesis in liver of diabetic rat

The effect of phenobarbitone on liver weight, on the rate of protein synthesis and on the sedimentation profiles of polyribosomes from livers was studied in diabetic rats. The rate of protein synthesis by isolated postmitochondrial supernatants from diabetic rats is lower than that from normal animals. The analysis of polyribosome profiles and the effect of Sephadex chromatography on protein synthesis demonstrated that the reduction was dependent in part on polyribosomal disaggregation and in part on the presence in the cytosol of low molecular weight inhibitor(s). Phenobarbitone administration had the same effect in either diabetic or normal rats in that it increased, (a) the degree of polyribosomal aggregation, (b) the rate of protein synthesis by the isolated postmitochondrial supernatants, (c) liver weight and (d) the activity of the inducible enzyme, NADPH-cytochrome c reductase. Both polyribosomal and soluble factors appear to be involved in the phenobarbitone effect. As the diabetic rats do not secret insulin the results suggest that insulin is not involved in the control of protein synthesis by phenobarbitone. It is suggested that the intracellular redox state has a major influence on the rate of protein synthesis.