[Quantitative morphology of megakaryocytes, with special reference to sex]

In dd-mice of both sexes, megakaryocytes in the spleen and bone marrow were quantitatively examined by light and electron microscopy particularly in relation to sex. In the splenic red pulp, megakaryocytes increase in number in early life until 35 days of age in both sexes. At 70 and 150 days of age, the megakaryocyte count is significantly greater in females than in males. Thus a significant sex difference is apparent between the two sexes in adult mice. Removal of the testis causes an increase of splenic megakaryocytes in number. In males, gonadectomized or normal, estrogen induces a marked increase in the number of megakaryocytes, whereas neither testosterone nor progesterone causes significant changes. In females, splenic megakaryocytes show a marked increase during pregnancy. After delivery, they gradually decrease in number. The decrease is more rapid in non-lactating than in lactating mice. In the bone marrow, megakaryocytes are almost similar in behavior to those in the spleen. The platelet count in peripheral blood is significantly increased in pregnancy, but not by estrogen. Electron microscopy reveals that splenic megakaryocytes are various in appearance depending on maturation. The quantitative morphologic results of the nuclei of megakaryocytes suggest that the increase of splenic megakaryocytes induced by estrogen or pregnancy is due to increase of immature megakaryocytes. The results obtained were discussed in particular relation to sex.