Amino acid concentration in the interstitium of human skeletal muscle: a microdialysis study

The microdialysis technique has been widely used for in vivo monitoring of the interstitial composition of several tissues. Remarkably high concentrations of taurine and glycerol were reported in a recent human study. As taurine and glycerol are predominantly present in the intracellular space, cellular trauma after probe insertion may have resulted in elevated interstitial concentrations. With the present study we wanted to investigate the impact of the initial trauma on the interstitial concentrations of amino acids and glycerol.

Microdialysis probes were inserted into the vastus lateralis muscle in eight subjects. Using a slow perfusion rate of 0.3 muL min-1, dialysate samples were collected in five 75-min periods. Simultaneously, plasma samples were taken from a peripheral vein for amino acid determination.

During the first collection period, the dialysate concentration for 21 measured amino acids was on average 180% +/- 51% higher than the concentration in plasma water. This difference decreased to 52% +/- 15%, 32% +/- 8%, 37% +/- 8% and 31% +/- 7% during periods 2, 3, 4 and 5 respectively. Carnosine, which is not present in plasma, was detected in high concentrations in the interstitium during the first collection period and decreased subsequently.

In the post-absorptive phase, the concentrations of most amino acids in muscle interstitium are slightly higher than in venous plasma water. The leakage of intracellular amino acids, because of probe insertion, will initially lead to an overestimation of the actual interstitial concentration of amino acids. Therefore, reliable baseline values of amino acids cannot be obtained until 120-150 min after probe insertion. The dialysate concentration of carnosine may be used as a marker of cellular leakage.