Free amino-acid levels simultaneously collected in plasma, muscle, and erythrocytes of uraemic patients.

BACKGROUND Disturbances in amino acid (AA) metabolism in uraemia have mainly been reported to occur in plasma and muscle. The erythrocytes (RBC) constitute a large proportion of the free AA in blood and may play an important role in the interogan transport of AA. This report presents the first data on AA levels obtained simultaneously from three different compartments in uraemic patients. METHODS Muscle biopsy and blood samples were obtained from 38 haemodialysis (HD), 22 continuous peritoneal dialysis (CPD) and 10 end-stage renal failure patients for determination of free amino acids by reversed-phase HPLC. The results are compared to data obtained from 27 healthy subjects under the same conditions. RESULTS For a number of non-essential AA (alanine, glycine, asparagine, arginine) and for lysine, elevated concentrations were present simultaneously in RBC and in muscle but not in plasma. On the other hand, low concentration of some essential AA (leucine, valine, phenylalanine, tyrosine) were observed in RBC and in plasma, while the concentrations in muscle were normal. Most of the non-essential AA (NEAA), especially taurine and glutamine, had much higher muscle/plasma gradients than RBC/plasma gradients, although an accumulation in RBC of glycine, serine, arginine, asparagine, ornithine, glutamate and taurine was observed. Most of the essential AA (EAA) showed higher muscle/plasma gradients, whereas the RBC/ plasma gradients were approximately 1.0. CONCLUSION Our findings are in agreement with studies that have shown that RBC and plasma play independent and opposing roles in AA interorgan transport. The results indicate that there are several AA abnormalities in all three compartments in uraemic patients. They also suggest that there may be some specific common changes of selected transport systems for both RBC and muscle in uraemia. Determination of AA in RBC should be considered when undertaking metabolic and clinical studies of AA disturbances.