The effect of branched-chain amino acid (BCAA) on protein synthesis and nitrogen metabolism in liver and skeletal muscle was evaluated by an intraperitoneal injection of [
15N]ammonium chloride (
15NH
4Cl) to carbon tetrachloride (CCl
4)-intoxicated rats. The
15NH
4Cl was bolusly injected at a dose of 6mg/100g body weight one hour after an amino acid solution containing leucine and valine (150mM each, abbre-viated as BCAA), phenylalanine and alanine (150mM each, PA), 120mM leucine and 30mM valine (Leu-rich) or 120mM valine and 30mM leucine (Val-rich) was administered intragastrically at a dose of 2.5ml each 100g body weight. The
15N-enrichment in the protein fraction of the liver was higher in CCl
4-BCAA group than CCl
4-PA group. The Leu-rich solution was found more effective in enhanced incorporation of
15N into liver and skeletal muscle proteins. The disappearance rate of [
15N]urea from the plasma, which was influenced by the synthesis from
15NH
3 and the excretion into urine, was much faster in the CCl
4-BCAA group than CCl
4-PA group. In Leu-rich group, both
15N incorporation into non-protein fraction of skeletal muscle and disappearance rate of plasma urea-1
15N were greater than those in Val-rich group. The results suggest that BCAA, particularly leucine, has beneficial effects on protein synthesis and am-monium detoxification in liver-injured rats.
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