Megakaryocytopoiesis in the spleen of growing rats

Age-dependent changes in splenic megakaryocytopoiesis of Wistar rats, 1 hour to 60 days old, were investigated using autoradiograms of semi-thin sections. The highest values for 3H-thymidine labeling and mitotic indices were observed immediately after birth, whereas the maximal concentration of megakaryocytes was seen on the 14th day after birth. The transit time of megakaryocytes in newly born rats was 34.5 hours and, thus, much shorter than in adult animals.