No abstract

The changes effected by injection of an extract of phospholipids obtained from the plasma of normal human donors (PLE) or an emulsion of commercially available sphingolipids on erythropoiesis in the mouse were studied. The parameters followed were 59Fe uptake by the erythroid tissue and the number of circulating reticulocytes. It was found that in the 12--24-h period following administration of PLE or purified sphingomyelin a significant increase in 59Fe uptake by circulating RBC an by their hemic fraction takes place. This change was associated with a higher 59Fe utilization by the bone marrow and with an increase in the number of circulating reticulocytes.

Removal of 15% of blood volume in the mouse increases erythropoiesis by a factor of 2.2 when measured 12 h after bleeding. Exposure of normal mice to 40% reduced barometric pressure for the same period of time increases erythropoiesis only by a factor of 1.6. The response to hypoxia takes place in the presence of a 40% reduction of oxygen consumption and tissue-venous PO2, changes which are concomitant with a 5-fold increase in plasma erythropoietin activity. The larger response in anemic animals on the other hand occurs without any detectable change in these parameters. These results cast serious doubts about the interpretation of the quantitative homeostatic control of erythropoiesis based solely on the action of erythropoietin.

Administration of phytohemagglutinin to protein-fasted and polycythemic mice results in a striking increase of spleen response to erythropoietin. An opposite ef- s feet was found in bone marrow. In transplant experiments, treatment of prospective cells donors with phytohemagglutinin produces a substantial increase of the cloning efficiency of the spleen cells with little if any effect on bone marrow cells. Results of this study also demonstrate a good correlation between the time course of cytomorphological changes induced by phytohemagglutinin on spleen lymphocytes and increase of hemopoietic stem cell concentration in this organ.