Different molecular weight of the plasmatic erythropoietin compared with the renal and splenic erythropoietic factors in the rabbit.

The authors have studied the molecular weight of the erythropoietic factors present in the blood, in the kidney and in the spleen of the rabbit, by means of ultrafiltration experiments performed by using selective-permeability membranes. The erythropoietic factor present in the blood circulation shows a molecular weight of between 10,000 and 30,000. The factors detectable in the microsomal fraction of normal kidney, in the mitochondrial fraction of anaemic kidney and in the mitochondrial fraction of normal spleen show molecular weights of between 50,000 and 100,000. These data confirm the hypothesis already formulated regarding the renal origin of the splenic erythropoietic factor and the different nature of the renal erythropoietic factor compared with the plasmatic erythropoietin.