PLASMA FOLATE CONJUGASE ACTIVITIES AND FOLATE CONCENTRATIONS IN PATIENTS RECEIVING HEMODIALYSIS

Folate conjugase activities and folate concentrations in blood obtaine d from patients with chronic renal failure and healthy controls were m easured by radioassay using pteroyldiglutamyl-[C-14]-glutamic acid as substrate and microbiologic assay, respectively. A total of 32 patient s receiving hemodialysis for an average of 5.4 years participated in t he study. Folate conjugase activities in posthemodialysis plasma were significantly higher than those in prehemodialysis samples and were si milar to those of controls. Plasma folate conjugase was inhibited by t he in vitro addition of the heated extract of prehemodialysis plasma. The heated extract of urine from a healthy control also inhibited the enzyme. Furthermore, plasma folate conjugase activities were reduced b y the in vitro addition of sulfate, one of the major constituents in u rine, although of urea or uric acid had no such effect. Data indicate the presence of an unidentified heat-stable inhibitor(s) that is excre ted by the normal kidney, and sulfate may be one of them. During hemod ialysis, plasma folate concentrations decreased, while erythrocyte fol ate concentrations remained unchanged. Five of 32 patients demonstrate d plasma folate concentrations lower than normal. These findings sugge st that a careful evaluation of folate requirements is necessary in pa tients maintained with hemodialysis.