[Demonstration of an erythropoiesis inhibiting factor with low molecular weight]

In saline incubation media of normal human erythrocytes after 20 hours at 37 degrees C a factor is demonstrable which inhibits 59iron incorporation into mouse erythrocytes, as well as 3H-thymidine incorporation into fetal mouse erythroblasts in vitro. Ultrafiltration of this erythropoiesis-inhibiting factor (EIF) showed a molecular weight of less than 10,000 dalton. After gel filtration (Sephadex G 50) the maximum activity of the EIF was found in the fractions which eluted closely before vitamin B 12 (1250 dalton), indicating a similar molecular weight. The EIF is heat stable (100 degrees, 10 min.) and seems to be a peptide. The inhibiting activity, measured by thymidine incorporation, is strong against mouse erythroblasts and lacking against lymphatic cells. A weak inhibition--possibly a toxic effect--on myelopoiesis cannot be excluded. The inhibition of mouse erythroblasts is reversible. In serum of normal subjects EIF was not demonstrable, whereas it was found in normal urine, indicating rapid renal elimination. This EIF, which is demonstrable under physiological circumstances, is suggested to be the erythrocytic chalone and furthermore could play a role in the production of anaemia in terminal renal failure.