Submitted on November 9, 2006
Accepted on January 29, 2007
AMINO ACID REPLETION DOES NOT DECREASE MUSCLE PROTEIN CATABOLISM DURING HEMODIALYSIS
Dominic SC Raj1*, Oladipo Adeniyi2, Elizabeth Ann Dominic3, Michel Andre Boivin4, Sandra Mcclelland5, Antonios H Tzamaloukas6, Nancy Morgan7, Lawrence P Gonzales7, Robert Wolfe8, and Arny Ferrando8
1 Division of Nephrology, University of New Mexico, Albuquerque, New Mexico, United States
2 Internal Medicine/Nephrology, University of New Mexico, Albuquerque, New Mexico, United States
3 Albuquerque Academy, Albuquerque, New Mexico, United States
4 Medicine, UNM HSC, Albuquerque, New Mexico, United States
5 General Clinical Research Center, University of New Mexico, Albuquerque, New Mexico, United States
6 Interternal Medicine/Nephrology, University of New Mexico, Albuquerque, New Mexico, United States
7 College of Pharmacy, University of New Mexico, Albuquerque, New Mexico, United States
8 Department of Geriatrics, University of Arkansas, Little Rock, Arkansas, United States
* To whom correspondence should be addressed. E-mail: draj{at}salud.unm.edu.
Intra-dialytic protein catabolism is attributed to loss of amino acids in the dialysate. We investigated the effect of amino acid infusion during hemodialysis (HD) on muscle protein turnover and amino acid transport kinetics using stable isotopes of phenylalanine, leucine and lysine in eight patients with end-stage renal disease (ESRD). Subjects were studied at baseline (Pre-HD), two hours of HD without amino acid infusion (HD-O) and two hours of HD with amino acid infusion (HD+AA). Amino acid depletion during HD-O augmented the outward transport of amino acids from muscle into the vein. Increased delivery of amino acids to the leg during HD+AA facilitated the transport of amino acids from the artery into the intracellular compartment. Increase in muscle protein breakdown was more than the increase in synthesis during HD-O (46.7% vs. 22.3%. p<0.001). Net balance (nmol/min-1.100 ml leg-1) was more negative during HD-O compared to pre-HD (-33.7±1.5 vs. -6.0±2.3, p<0.001). Despite abundant supply of amino acids, the net balance (-16.9±1.8) did not switch from net release to net uptake. HD+AA induced a proportional increase in muscle protein synthesis and catabolism. Branched chain amino acid catabolism increased significantly from baseline during HD-O and did not decrease during HD+AA. Protein synthesis efficiency, the fraction of amino acid in the intracellular pool that is utilized for muscle protein synthesis decreased from 42.1% pre-HD to 33.7% and 32.6% during HD-O and HD+AA respectively (p<0.01). Thus, amino acid repletion during HD increased muscle protein synthesis, but did not decrease muscle protein breakdown.
