Mechanisms of local regulation of erythropoiesis within bone marrow erythroblastic islands in rats

Abstract

The purpose of the study was to examine the mechanism of macrophage involvement in erythropoietic process within bone marrow erythroblastic islands (EI). Changes of the tissue oxygen supply following removal of blood cells (2% BW) or transfusion of 2.5ml/100g BW of a 70% suspension of washed isogenous red cells/2days were modeled in rats. Plasma erythropoietin level (by RIA), the total number of EI/femur and specific indices of erythropoiesis, based on EI of different classes of maturity were estimated during a 10-day period. In bled animals the initial decrease in hematocrit was accompanied by an increased number of absolute EI/femur—628.3±102×103/femur (day 3) vs. 406.7±169×103/femur (P<0.01) and proliferating EI appeared elevated on days 3–7. The rate of CFU-E differentiation into erythroblasts in EI and the rate of repeated participation of macrophages in new EI reconstruction were increased during the first days after bleeding (P<0.05). Polyglobulia in hypertransfused rats was accompanied by a significant attenuation of EI formation. The number of islands was a 135.6±25×103/femur (day 5) vs. 347.6±65×103/femur (P<0.001) in controls. A persistent reduction of young and reconstructive islands, and of the related indices of erythropoiesis was observed. The role of macrophages to organize islands of different classes of maturity was estimated. Our results support the assumption about the specific regulatory role of the centrally-situated macrophages. Macrophage-erythroblast interactions were influenced by the oxygen supply to the tissues after stimulation of reduction of erythropoiesis.