The increased skeletal muscle protein turnover of the streptozotocin diabetic rat is associated with high concentrations of branched-chain amino acids

Experimental streptozotocin-induced diabetes resulted in important changes in body weight which were associated with abnormalities in water and food intake. In addition, diabetic rats showed a clear muscle atrophy involving a decrease in both skeletal muscle size and protein content. This was accompanied by a marked loss of total carcass nitrogen. These changes were related to important alterations in protein turnover in skeletal muscle. Thus, the diabetic animals showed changes in the fractional protein rates of both synthesis (decreased by 37%) and degradation (increased by 140%). The increased protein degradation observed in the muscle of the diabetic animals was associated with important changes in the concentration of both circulating and muscle amino acids. Interestingly, the diabetic animals did not show important changes in either liver or kidney protein turnover rates, in spite of having a clear increase (over 50%) in kidney mass. In addition, and although the total amino acid concentration was not affected by the diabetic state, the chemically induced diabetic animals showed important elevations of branched-chain amino acids (leucine, isoleucine, and valine) in both blood and skeletal muscle. Similarly, important decreases in the blood concentrations of glutamate+glutamine, alanine, glycine, proline, serine, and threonine were also observed. These observations reinforce the idea of the association between muscle protein wasting, increased protein turnover, and alterations in branched-chain amino acids previously proposed by our group.