Key Role of Various Individual Amino Acids in Host Response to Infection.

摘要

During infections in man the pattern of change in individual plasma free amino acids is markedly different from that observed in simple starvation. Plasma phenylalanine and tryptophan are both increased in bacterial or viral infections. This increase is correlated with an accelerated rate of release of these amino acids from skeletal muscle. Alanine is also released in increased amounts by skeletal muscle but is utilized rapidly by liver for gluconeogenesis to meet the accelerated rates of glucose turnover and oxidation in the infected host. The rate of release of the branched chain amino acids from the muscles of infected rats is decreased, which results in depression of their plasma concentrations. These data have been interpreted to suggest that during infection, protein catabolism in skeletal muscle is increased and amino acids such as those of the branched chain group are utilized as energy sources or for the synthesis of alanine or glutamine. Those amino acids, such as phenylalanine and tryptophan, which cannot be metabolized in skeletal muscle are released in elevated amounts, as are alanine and glutamine, which have been synthesized from other amino acids. The alanine is rapidly taken up by the liver and utilized as a substrate for gluconeogenesis. Because the infected host has an impaired ability to develop starvation ketosis, it continues to break down muscle protein as a source of energy and substrates for glucose synthesis. (Author)