Erythropoietin and uremic toxicity during continuous ambulatory peritoneal dialysis

This study examined the effect of continuous ambulatory peritoneal dialysis (CAPD) on erythropoiesis and macrophage function. The parameters evaluated were hemoglobin, erythropoiesis-stimulating factor(s) (ESF), and the inhibitory effect of patients' plasma and peritoneal dialysate on erythropoiesis in vitro and on the function of macrophages from normal humans cultured in vitro. ESF was determined by a cell culture assay using hepatic erythroid colony forming cells (CFUE) from newborn mice. The uremic inhibitory effect on macrophages cultured in vitro was expressed as macrophage survival in percentage of controls. Five patients were studied, one of whom was anephric. Hemoglobin increased, without blood transfusions during CAPD treatment, suggesting improved erythropoiesis. Plasma ESF increased in all patients; dialysate ESF increased in all but one patient. Survival of macrophage in vitro, incubated with plasma or dialysate, also improved. In two patients, the inhibitory effect of plasma samples on erythropoiesis in vitro decreased during CAPD treatment. These observations indicate that CAPD removes inhibitors of erythropoiesis and human macrophage function in vitro, and are consistent with transport of inhibitory substances of high molecular weight into the peritoneal cavity. The anephric patient showed improvement of erythropoiesis similar to that of the nephric patients, indicating that the kidney may not be the main producer of erythropoietin (Ep) in patients undergoing CAPD. Peritoneal macrophages may be a site of extrarenal Ep production in this situation. With regard to the parameters studied, CAPD treatment is superior to conventional hemodialysis.