Effects of pregnancy on erythropoiesis in the splenic red pulp of the mouse: a quantitative electron microscopic study.

The effects of pregnancy on erythropoiesis in the splenic red pulp of the mouse was examined quantitatively by electron microscopy. In the red pulp of a normal female at 60 days of age, erythroid cells were most numerous, constituting 73.3% of all the hemopoietic cells, and 55.1% of the erythroids were erythroblasts. By quantitative stereology, erythroblasts could be classified by nuclear size into three classes: small, medium and large. Out of all the erythroblasts small erythroblasts constituted 50%, medium erythroblasts 35%, and large erythroblasts 15%. The relation of the nuclear volume of large, medium and small erythroblasts was approximately 4 : 2 : 1. In pregnancy erythroids, particularly erythroblasts, increase markedly in number. The estimated total number of erythroblasts in the red pulp was 3.8 x 10(7) for the normal, 9.7 x 10(7) at 5 days of pregnancy, and 17.4 x 10(7) at 15 days. In early pregnancy, large and medium erythroblasts increased more markedly than small ones, while in late pregnancy not only large and medium but also small erythroblasts were much increased in number. At 20 days postpartum, erythroblasts had returned to normal in number and proportion of each class. The quantitative stereological approach proved to be useful for assessing erythropoietic activity in the splenic red pulp.