The Sustained Action of Erythropoietin Injected Repeatedly into Rats and Mice

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Abstract
Rats and mice were given exogenous erythropoietin for periods from 40 to over 200 days. Increased erythropoiesis was maintained as long as erythropoietin was given; when it was stopped, erythropoiesis returned to its normal level; when the dose was dimished, erythropoiesis fell accordingly. In mice there was no long-term increase of platelets or change in the differential leukocyte counts and leukocyte counts were, during the middle period of the experiment, decreased. One mouse developed a tumor. It is pointed out that humans with certain chronic anemias have lived for years with greatly elevated concentrations of erythropoietin in their blood and urine, yet they have normal leukocyte and platelet counts and no tumors.