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-prot ein-bound free form (FTrp) and its metabolite 5-hydroxyindole-3-acetic acid (5-HIAA) as well as muscle Trp contents (MTrp) were studied in 1 2 uraemic patients undergoing continuous ambulatory peritoneal dialysi s (CAPD), 10 renal transplant patients, and 10 healthy control subject s. The CAPD patients exhibited signs of muscle weakness, as assessed b y dynamometry, and signs of protein malnutrition with a decreased rati o of alkali-soluble protein relative to DNA in muscle as well as low s erum 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 pati ents (P<0.01) than in the controls. The plasma FTrp/TTrp ratio was inc reased in the uraemic patients (40+/-8%) but less in the transplant pa tients (16+/-4%), as compared to the controls (25+/-5%). The uraemic p atients had increased plasma concentrations of 5-HIAA, whereas this me tabolite 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 pati ents and the controls. The results indicate that the abnormal Trp meta bolism in uraemic patients is to a large extent corrected by a success ful renal transplantation. The increased MTrp in CAPD patients would s uggest that the marked reduction in the plasma Trp, TTrp, and FTrp ref lects a shift from the extra- to the intracellular space rather than a depletion of Trp.