Effect of proportion of three branched-chain amino acids (leucine, valine, and isoleucine: BCAA) for nitrogen utilization was studied in vivo by an intragastric administration of
15N-L-leucine to control rats and liver-injured rats treated with carbon tetrachloride (CCl
4-rats). Following the administration of isonitrogenous dose of three amino acid solutions [Standard (i 5N-L-leucine, L-valine, L-isoleucine, and L-alanine; 11, 8, 6, 18 mg/ml), Low-Val (11, 2, 6, 23 mg/ml), and High-Val (11, 32, 6, 0 mg/ml)],
15N enrichments in serum albumin, liver, skeletal muscle, and brain proteins and non-protein fractions, and urea nitrogen were compared by using
15N-analyzer. In CCl
4-rats, the
15N enrichment in liver protein fraction was significantly lower in the High-Val group than in the Low-Val group. However, the difference of
15N enrichment in serum albumin between Low-Val and High-Val groups in CCl
4-rats was unclear. The
15N enrichments in non-protein fractions of the brains in CCl
4-rats were about twofold those in the skeletal muscles and the highest
15N enrichment was recognized in the Low-Val group. In the non-protein fraction of skeletal muscle in CCl
4-rats, significantly low
15N enrichment was shown in the High-Val group compared with the Low-Val group. The
15N enrichment in urinary urea was significantly higher in the High-Val group than in the Low-Val group in CCl
4-rats. In the Standard group of control rats,
15N enrichments in serum albumin and protein fraction of skeletal muscle were higher than in other groups. In non-protein fractions of control rats, the lowest
15N enrichment in liver and the highest
15N enrichment in skeletal muscle were recognized in the Standard group. These results suggest that a large amount of valine supplement among BCAA is less useful for leucine utilization in liver-injured rats than in normal rats.
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