Vormann et al.: Erythrocytc magnesium metabolism in chronic renal failure 901 Eur. Summary: Plasma and erythrocyte Mg 24 " concentrations were found to be increased in 14 haemodialysis patients with chronic renal failure and in 7 chronic renal failure patients receiving chronic ambulatory peritoneal dialysis. The rate of Na+TMg 2 * antiport was significantly higher in haemodialysis patients, but not in chronic ambulatory peritoneal dialysis patients (control: 0.15 ± 0.02, haemodialysis: 0.46 ±

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... .08, chronic ambulatory peritoneal dialysis: 0.21 ± 0.06; Mg 2 " 1 ", mmol/30 min X l cells). High erythrocyte Mg 2+ content in chronic renal failure results from the increased plasma Mg 2+ , which induces elevated Mg 2 " 1 " uptake during haematopoiesis. An increased rate of Na + /Mg 2+ antiport, which only performs Mg 2+ efflux, leads to a relatively lower erythrocyte Mg 2+ content in haemodialysis patients compared with chronic ambulatory peritoneal dialysis patients. The elevated Na + /Mg 24 " antäport in erythrocytes from haemodialysis patients was almost normalised after haemodialysis. Incubation of normal erythrocytes with heat-inactivated plasma from haemodialysis patients led to a doubling of Na + /Mg 2+ antiport, indicating the presence of a heat-stable, dialysable plasma factor. This factor does not accumulate in chronic ambulatory peritoneal dialysis patients. After renal transplantation all changed quantities of Mg 24 " metabolism returned to normal.