Adaptation of Uraemic Patients to Anaemia: A31 P Nuclear Magnetic Resonance Study

: It is well established that ESRD patients can tolerate a greater degree of anaemia than anaemic subjects of other aetiologies. It is widely accepted that this is partly due to a decrease in the oxygen affinity of haemoglobin (Hb) associated with a greater concentration of 2,3-diphosphoglycerate (2,3-DPG) observed in uraemic patients. In order to verify whether this is a concentration effect or whether the binding of 2,3-DPG in erythrocytes is structurally affected, we have studied 2,3-DPG haemoglobin binding by measuring spin-spin relaxation times (T2) of 31P in living erythrocytes (RBC) by NMR. In uraemic RBC, 2,3-DPG relaxation is faster. This difference is not due to the reduced intracellular pH of uraemic RBC: we have verified that increased presence of paramagnetic substances can also be discarded since intra-RBC proton T2 is longer. Our results are compatible with stronger binding of 2,3-DPG to haemoglobin in uraemic erythrocytes, stabilising the deoxyhaemoglobin form and therefore facilitating oxygen release.