Tryptophan and its metabolites in patients on continuous ambulatory peritoneal dialysis and following renal transplantation.

Plasma tryptophan (Trp) concentration in its total (TTrp) and non-protein-bound free form (FTrp) and its metabolite 5-hydroxyindole-3-acetic acid (5-HIAA) as well as muscle Trp contents (MTrp) were studied in 12 uraemic patients undergoing continuous ambulatory peritoneal dialysis (CAPD), 10 renal transplant patients, and 10 healthy control subjects. The CAPD patients exhibited signs of muscle weakness, as assessed by dynamometry, and signs of protein malnutrition with a decreased ratio of alkali-soluble protein relative to DNA in muscle as well as low serum albumin concentration. In the uraemic patients TTrp was markedly reduced, whereas in the transplant patients it did not differ from the controls. The FTrp, which was separated by the process of equilibrium dialysis, was less in the uraemic (P < 0.01) as well as transplant patients (P < 0.01) than in the controls. The plasma FTrp/TTrp ratio was increased in the uraemic patients (40 +/- 8%) but less in the transplant patients (16 +/- 4%), as compared to the controls (25 +/- 5%). The uraemic patients had increased plasma concentrations of 5-HIAA, whereas this metabolite could not be found in the plasma of renal transplant patients and healthy controls. MTrp was increased by an average of 33% in the uraemic patients whereas it did not differ between the transplant patients and the controls. The results indicate that the abnormal Trp metabolism in uraemic patients is to a large extent corrected by a successful renal transplantation.(ABSTRACT TRUNCATED AT 250 WORDS)