Mechanisms of Plasma Hemoglobin Clearance after Acute Hemolysis in Dogs

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Abstract
Mechanisms of removal of free hemoglobin from the circulating plasma were studied experimentally in dogs, employing Cr51 labelled hemoglobin. Free hemoglobin combined primarily with available circulating haptoglobin and this molecule presumably was removed from the plasma by the reticulo-endothellal system in the liver and spleen. Further accumulation of free hemoglobin, beyond the combining power of haptoglobin, resulted in hemoglobinuria, but only when levels of free hemoglobin of approximately 70 mg% or more were present in the plasma. Even then, the percentage of available free hemoglobin actually excreted by the kidneys was small and the kidneys did not appear to act as effective excretory organs for free hemoglobin. Most free hemoglobin, above the combining power of haptoglobin, was removed from the plasma by deposition in various body tissues but chiefly in renal cortex. Progressively higher levels of free plasma hemoglobin resulted in a selective proportionate increase in hemoglobin deposition in the kidneys. Hemoglobin deposited in liver and kidney was remobilized steadily and fell to immeasureable levels by approximately 100 days, as indicated by tissue radioactivity levels.