Intradialytic
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 by using stable
isotopes of
phenylalanine,
leucine, and
lysine in eight patients with
end-stage renal disease (
ESRD). Subjects were studied at baseline (pre-HD), 2 h of HD without
amino acid infusion (HD-O), and 2 h 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 (-1)) was more negative during HD-O compared with pre-HD (-33.7 +/- 1.5 vs. -6.0 +/- 2.3, P < 0.001). Despite an 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.