Effect of hemodialysis on protein synthesis.

BACKGROUND

Earlier studies have shown that hemodialysis (HD) treatment stimulates net protein catabolism. Several factors associated with HD affect protein catabolism, such as an inflammatory effect due to blood-membrane contact and loss of amino acids and glucose into the dialysate.

SUBJECTS, MATERIAL AND METHODS: We have studied protein synthesis in skeletal muscle of healthy volunteers (n = 9) before and after a single heparin-free HD. Protein synthesis (PS) was studied, using 2 independent techniques: the incorporation of labeled 2H5-phenylalanine into muscle protein, which gives a quantitative measure of the fractional synthesis rate of muscle proteins, and the concentration and size distribution of ribosomes, which gives a qualitative estimate of protein synthesis. Furthermore, free amino acid concentrations were determined in muscle and plasma.

RESULTS

The rate of PS, expressed as the fractional synthesis rate, decreased by 13% during HD (p < 0.02). The capacity for PS, as reflected by the total concentration of ribosomes, was reduced by 22% (p < 0.02) and the activity of PS, expressed as the relative proportion of polyribosomes, decreased from 48.4 +/- 0.9% to 44.8 +/- 0.8% after dialysis (p < 0.01). There was a total loss of 5.8 +/- 0.3 g amino acid to the dialysate. Plasma and muscle free amino acid concentrations were determined at four time points; before and after the phenylalanine incorporation period, before dialysis and before and after the second incorporation period after dialysis. Immediately after dialysis, there was a decrease in plasma asparagine, histidine, alanine, taurine, valine and tryptophane. In muscle, no changes occurred except for a slight increase in leucine after dialysis. In blood, the glucose concentration decreased and the total amount of glucose lost to the dialysate was 21 +/- 3.0 g. In summary, one single hemodialysis treatment decreases fractional protein synthesis rate in skeletal muscle.

CONCLUSION

The results demonstrate substantial losses of amino acids and glucose to the dialysate and decreased amino acid concentrations in plasma, but only minimal changes in the intracellular amino acid concentrations in muscle, suggesting that the decreased PS is caused not by lack of amino acid precursors at the site of the synthesis activity, but by other mechanisms.