Abstract
The assumption that inability to extract erythropoietin from the kidney is due to a renal lipid inhibitor, which inactivates the hormone during the process of extraction, has been substantiated. Discovery of erythropoietic inhibitory activity in the spleen and liver prompted this comparative study of other extrarenal tissues for erythropoietic inhibitory factor but also as a means of examining organ specificity for binding the hormone. Rabbit stomach lipid extracts proved to be even more active against erythropoietin than kidney extract. Other tissues exhibited moderations of erythropoietic inhibitory activity, though brain and subcutaneous fat were decidedly inactive against erythropoiesis. However, this hypothesis must rest on reproducible in vivo assessment of the inhibitor.