| Abstract: | The usefulness of hemoglobin solutions as plasma expanders with oxygen-carrying capacity is limited by a high oxygen affinity and a rapid clearance from the circulation. A large amount of the hemoglobin is cleared by the kidneys, because the hemoglobin can pass the glomeruli after dissociation into dimers. This dissociation can be prevented by cross-linking the beta chains with 2-nor-2-formylpyridoxal 5'-phosphate (NFPLP), a modification that also diminishes the oxygen affinity. In the present study, the vascular retention of modified hemoglobin (HbNFPLP) compared with unmodified hemoglobin (Hb) was investigated in rats and rabbits by replacing half the blood volume with a mixture of Hb and HbNFPLP (7 gm/100 ml). The amount of free hemoglobin in the circulation was determined from the plasma concentration, corrected for the decrease in plasma volume. The decrease in plasma volume was calculated from the increase in hematocrit (in the rats, 30% to 40% in 3 hours). The ratio Hb/HbNFPLP was determined by high-performance anion-exchange chromatography. The half-disappearance times for HbNFPLP and Hb were found to be 3 hours and 1 hour in rats and 7 hours and 2.5 hours in rabbits, respectively. In the rats, one third of the unmodified Hb was found in the urine 5 hours after the exchange, against only 5% of the HbNFPLP. In rats without kidneys, the ratio of Hb/HbNFPLP in the circulation remained constant. The results demonstrate that intramolecular cross-linking of hemoglobin with NFPLP prevents excretion by the kidneys, but does not influence other clearance mechanisms. |
