Plasma and Skeletal Muscle Free Aminoacids in Acute Renal Failure
Abnormalities in protein metabolism are well known in acute renal failure (ARF) (1, 2). When renal function is acutely reduced or completely abolished, two phenomena contribute to derange protein metabolism: first, acute protein catabolism occurs inducing negative nitrogen balance, overproduction of urea and other nitrogen catabolites; second, these latter substances accumulate in the body, due to defective renal excretion, possibly contributing through their toxic effect to enhance proteolysis. In addition, if ARF is accompanied or is caused by catabolizing events (severe bleeding, surgery, sepsis, rhabdomiolysis), a further stimulus to protein breakdown contributes to a tremendous, acute malnutrition (1, 2). It is generally thought that the severity of protein catabolism may influence the clinical course of ARF (1). Acute malnutrition in ARF may be easily demonstrated by net loss of muscle mass (1, 2) and from a biochemical point of view by severely negative balance, fall of serum proteins and finally by changes in plasma amino acids (AA) levels, with reduction of essential AA (1). However, plasma free AA concentrations are not fully representative of the whole body pool of free AA, the concentrations of which are by far higher in intracellular water (ICW) than in plasma (3). Muscle tissue is the largest homogeneous cellular tissue in the body, thus containing the largest amount of free AA. Every catabolic condition is characterized primarily by increased net muscle protein degradation, which in turn causes increased flow of free AA to other organs, mainly to the liver. Accelerated muscle proteolysis is reflected also by changes in muscle free AA concentrations, as it has been demonstrated under several conditions, such as surgical trauma, sepsis, diabetes mellitus (4, 5, 6, 7). On the other hand it has been shown that sufficient and equilibrated concentrations of cellular free AA are needed to fully regulate equilibrium between muscle protein synthesis and breakdown (8).
KeywordsPlasma Amino Acid Acute Malnutrition Free Amino Acid Pool Negative Nitrogen Balance Free Amino Acid Concentration
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