Objective:
End-stage renal disease patients undergoing hemodialysis experience a rapid decline in skeletal muscle mass and strength. Hemodialysis removes amino acids from the circulation, thereby lowering plasma amino acid concentrations and stimulating muscle catabolism. In the present study we evaluate the impact of intradialytic protein ingestion at rest and following exercise on amino acid removal and plasma amino acid availability during hemodialysis.

Methods:
Ten end-stage renal disease patients (age: 65±16 y, BMI 24.2±4.8 kg/m², serum albumin: 3.4±0.3 g/dL) undergoing hemodialysis participated in this randomized crossover trial. During four hemodialysis sessions, patients were assigned to ingest 40 g protein or a placebo 60 min after initiation, both at rest (PRO and PLA, respectively) and following 30 min of exercise (PRO+EX and PLA+EX, respectively). Blood and spent dialysate samples were collected every 30 min throughout hemodialysis to assess amino acid concentrations and, as such, to quantify plasma amino acid availability and amino acid removal.

Results:
Plasma amino acid concentrations declined by 26.1±4.5% within 30 min after hemodialysis initiation in all treatments (P<0.001). During PLA and PLA+EX treatments, subsequent plasma amino acid concentrations decreased even further (P<0.05). This resulted in a similar low amino acid availability (iAUC) throughout PLA and PLA+EX treatments (-227±54 and -208±68 mmol/L/240 min, respectively; P=0.43). Plasma amino acid concentrations increased above baseline values following protein ingestion, with no differences in amino acid availability between PRO and PRO+EX treatments (49±87 and 70±34 mmol/L/240 min, respectively; P=0.42). Amino acid removal was greater during PRO and PRO+EX treatments (16.6±2.2 and 17.3±2.3 g, respectively) when compared to PLA and PLA+EX treatments (9.8±2.0 and 10.2±1.6 g, respectively; P<0.001)

Conclusion:
Intradialytic protein ingestion increases amino acid removal, but improves plasma amino acid availability and net protein balance throughout hemodialysis. Intradialytic exercise does not modulate amino acid removal during hemodialysis in a post-absorptive or post-prandial state.