Inhibition of Erythropoiesis by Plasma From Newborn Infants

Summary The marked and rapid decrease of erythropoie‐sis in the normal newborn infants may be due to disappearance of erythropoietin alone, but an inhibitory mechanism may also be involved. Several authors have previously reported the presence of erythropoiesis‐inhibiting factors in plasma from high altitude natives brought to sea level and in plasma from hypertransfused animals. The present studies of 59 Fe incorporation in RBC of polycythemic mice injected with plasma from normal and hyperbilirubinemic newborn infants, show that erythropoietic in‐hibitor(s) is present in the plasma of infants at least from the fourth day of life. This inhibition was not due to the bilirubin content. A possible influence of estrogen was discussed and found to be unlikely. The relation to chalones, the tissue specific inhibitors of mitosis, is discussed.