THE INCREASE IN MUSCLE GLUTAMINE CONCENTRATION IN HINDLIMBS OF TUMOR-BEARING RATS IS ASSOCIATED WITH FACILITATION OF ARGININE AND ORNITHINEUPTAKE

Our previous study showed that the muscle glutamine concentration was markedly elevated by administration of an arginine-enriched amino acid solution (AI-82) as a total parenteral nutrition (TPN) regimen in Yos hida sarcoma-bearing (TB) rats (1). Here, by using the same TPN model, we determined the net uptake/release of amino acids and several carbo hydrates from the hindlimbs of TB rats administered AI-82 by measureme nt of arteriovenous differences in order to estimate what kinds of ami no acids and substrates were utilized for glutamine synthesis in the h indlimbs compared with rats administered conventional amino acid solut ion (Proteamin12). AI-82 administration resulted in a marked enhanceme nt of the uptakes of arginine (P < 0.01) and ornithine (P < 0.001) in the hindlimbs when compared with Proteamin12 administraion. The uptake of BCAAs (leucine, isoleucine and valine) in the hindlimb, which were considered to provide to the muscle with nitrogen for the formation o f glutamine, tended to increase but not by statistically significant a mount. We also measured the urinary excretion of 3-methylhistidine thr oughout the experimental period in order to determine whether amino ac ids from protein degradation could be utilized for glutamine synthesis in the muscle. Significantly decreased muscle protein degradation, in terms of the 3-methylhistidine/creatinine ratio in the urine, was obs erved in the AI-82 group over the period of TPN. These results showed that increased muscle concentration of glutamine in the AI-82 group wa s not associated with muscle protein degradation but was partially ass ociated with uptake of exogenous BCAA nitrogen in the hindlimb. The si gnificant uptake of arginine and ornithine in the hindlimb in the AI-8 2 group was discussed in connection with the high level of glutamine i n the muscle.