The Role of Protein and Amino Acids in Sustaining and Enhancing Performance (1999) / Chapter Skim
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8 Infection and Injury: Effects on Whole Body Protein Metabolism
8 Infection and Injury: Effects on Whole Body Protein Metabolism
Pages 155-168
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From page 155... ...
National Academy Press 8 Infection and Injury: Effects on Whole Bocly Protein Metabolism Douglas W WiZmore~ Injury and infection elicit a rather stereotypic metabolic response characterized by hypermetabolism, accelerated gluconeogenesis, increased fat oxidation, and negative nitrogen balance (Wilmore, 1997~.
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This chapter outlines some of the changes that occur in whole body protein metabolism following infection and injury. Evidence will be presented that these catabolic states result in marked translocation of protein from the carcass to visceral tissues, resulting in a net loss of skeletal muscle mass.
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From these and related studies, some general conclusions can be made concerning the whole body protein catabolic response following injury or infection: · The increased nitrogen loss occurs via the urine. Urea represents the major component of the nitrogen lost and contributes 85 to 90 percent to the negative nitrogen balance.
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Precipitating Factor Cumulative Nitrogen Loss (g) Injuly Major burn Multiple injury Peritonitis Simple fracture Major operation Minor operation Infection Typhoid fever (untreated)
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Injury and infection result in the increased whole body flux of amino acids throughout the body. Catabolic rates outstrip rates of protein synthesis in the partially fed state; feeding enhances protein synthesis and attenuates the negative nitrogen balance that occurs.
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From page 160... ...
This represents accelerated de novo synthesis of these amino acids; hydrolysis and analysis of skeletal muscle protein reveals that both alanine and glutamine contribute less than 10 percent to the overall amino acid residues. Translocation of these amino acids to visceral tissues presumably occurs for a purpose; both amino acids serve as important glucose precursors and support the enhanced rate of gluconeogenesis.
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From page 161... ...
Hormonal infusion caused many, but not all, of the responses observed following infection and injury. Specifically, when glucagon, glucocorticoids, and catecholemines were infused to achieve blood levels similar to those that occur in catabolic states, negative nitrogen balance, hypermetabolism, and accelerated gluconeogenesis were observed (Bessey et al., 19841.
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From page 162... ...
that induce skeletal muscle proteolysis (Mitch and Goldberg, 1996) , alter carbohydrate metabolism, and stimulate hypermetabolism, all of which are components of the metabolic responses observed following injury and infection (Ling et al., 1997~.
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1979. Increased peripheral amino acid release following burn injury.
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1986. Both inflammatory and endocrine mediators stimulate host responses to sepsis.
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From page 165... ...
Vitamin E loading, in adequate doses, for example, takes about four weeks. And there are nice clinical data now from heart biopsies of patients undergoing cardiac surgery where various doses and time intervals have been used for vitamin E loading as an antioxidant.
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DOUGLAS WILMORE: Presumably it is there to protect circulating blood volume and oxygen delivery capacity. The mechanisms are through a lot of normal pathways that conserve salt and water.
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Do gender or age affect the metabolic response to injury in any way? DOUGLAS WILMORE: They must, but the age issue is exceedingly difficult to study because you introduce progressive organ dysfunction or change; you bring in other disease processes and things like that.
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