Studies on the Erythropoiesis Inhibiting Factor in the Plasma of Animals with Transfusion Polycythemia

Further investigations of the action of polycythemic plasma filtrate were made using Fe⁵⁹ and with detailed examination of the blood and bone marrow. These studies confirmed the appearance of an active thermostabile plasma factor (erythropoiesis inhibitor) which depressed erythropoiesis in normal rabbits or rats. The plasma obtained from bilaterally nephrectomized sheep subjected to transfusion polycythemia also contained the erythropoiesis inhibitor. Blockade of the reticuloendothelial system using trypan blue, in sheep, induced production of the active substance similar or identical with the erythropoiesis inhibitor produced after transfusion polycythemia.