Different Molecular Weight of the Plasmatic Erythropoietin Compared with the Renal and Splenic Erythropoietic Factors in the Rabbit

Abstract

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 sing selective-permeability membranes. The erythropoietic factor present in the blood circulation shows a molecular weight of between 10,000 and 30,000. The factors etectable in the microsomal fraction of ormal 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.

Activity of Inhibitors on Plasmatic Erythropoietin and on the Renal and Splenic Erythropoietic Factors in the Rabbit

“…All these data therefore show that the erythropoietic factors present in the kidney and in the spleen differ from the erythropoietin to be found in anaemic plasma and in kidney-normal plasma and spleen-normal plasma incubation mixtures, not only in their molecular weight, as recently dem onstrated [2], but also in other physicochemical characteristics.…”

“…It is therefore probable that it is to be identified with that described by Lewis et al [5,6] in the urine of anaemic patients: a hypothesis also sug gested by the results of other recent studies [2], The fact that in the same experimental conditions the DTT also inactivates the factor present in the spleen of the rabbit appears to be in agreement with the results of pre vious works, which show that there occurs, in the spleen, an accumulation of an erythropoietic factor produced and released into the circulation by the kidney [7,8].…”

“…These activities were assessed by studying the variations in the reticulocyte pat tern in the peripheral blood of rigidly selected rabbits, later treated with the various preparations under examination by following the criteria already described in pre vious works [2,3]. In particular, in the extraction tests for the various erythro-sti mulant factors, use was made of groups of 6 normal or bled donors, from which organs or plasma were removed, and, at the same time, of groups of 6 receivers, each of which was to be treated with the material obtained from a single donor.…”

Human Growth

“…The kidney responds to hypoxia by secreting a glycoprotein termed erythropoietin or an enzyme precursor of it. Its molecular weight has been stated to be about ± 65,000 (Goldwasser and Kung, 1968), but it now seems to differ according to the source from which the preparation is made (Giovannini and Bocchini, 1975). In adult dogs and rodents the kidney is preeminently its site of production (Kuratowska et ai., 1961;Krantz, 1970).…”