THE INCREASED SKELETAL-MUSCLE PROTEIN-TURNOVER OF THE STREPTOZOTOZIN DIABETIC RAT IS ASSOCIATED WITH HIGH-CONCENTRATIONS OF BRANCHED-CHAIN AMINO-ACIDS

Experimental streptozotozin-induced diabetes resulted in important cha nges in body weight which were associated with abnormalities in water and food intake. In addition, diabetic rats showed a clear muscle atro phy involving a decrease in both skeletal muscle size and protein cont ent. This was accompanied by a marked loss of total carcass nitrogen. These changes were related to important alterations in protein turnove r in skeletal muscle. Thus, the diabetic animals showed changes in the fractional protein rates of both synthesis (decreased by 37%) and deg radation (increased by 140%). The increased protein degradation observ ed in the muscle of the diabetic animals was associated with important changes in the concentration of both circulating and muscle amino aci ds. 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 st ate, the chemically induced diabetic animals showed important elevatio ns 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, proli ne, serine, and threonine were also observed. These observations reinf orce the idea of the association between muscle protein wasting, incre ased protein turnover, and alterations in branched-chain amino acids p reviously proposed by our group. (C) 1997 Academic Press.