Erythropoiesis in the spleen and bone marrow of the pregnant mouse

Abstract

The alterations in blood volume and in spleen and bone marrow erythropoiesis during pregnancy in mice of the C57BL 6J inbred strain have been explored. Blood volumes were shown to increase progressively, reaching 20% above nonpregnant levels by day 12 of gestation and an elevation of 75% at day 18. A progressive fall in hematocrit levels was observed to day 12, with lower than normal hematocrits maintained to term. Spleen weight doubled by day 12, and the spleen's content of nucleated cells increased 3- to 4-fold. Both size and cellularity decreased dramatically toward term. Spleen erythropoietic activity was measured both by Lepehne's staining for hemoglobin, of cells drawn from single-cell suspensions onto Millipore filters, and by uptake of 59Fe in short-term cultures. Splenic erythropoiesis increased sharply to a peak that represented a 40-fold increase by day 12; activity then declined markedly, coincident with the decline in spleen weight. Bone marrow erythropoietic activity increased moderately, reaching maximal values at day 12, and decreasing toward term. At the time of peak response, from days 11–13, the degree of anemia and the magnitude of splenic erythropoiesis were shown to depend directly upon litter size. The development of anemia was not prevented by injection of iron prior to mating, nor did the administration of iron prevent the dramatic drop in maternal splenic erythropoiesis between days 12 and 18 of gestation. Splenectomized mice were used to show that the spleen is not essential for the maintenance of erythropoietic homeostasis in pregnancy.