MEGAKARYOCYTES IN THE RAT SPLEEN

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Abstract
Spleens from rats, fetal to 3 years of age, were studied histologically with particular attention being directed toward the megakaryocytes. The number of megakaryocytes per unit area studied increased from the fetal stages to the 7th postnatal week and then decreased gradually until only a very few were found in year-old animals. Animals older than 2 years generally showed a slight increase in the number of megakaryocytes.These changes in splenic megakaryocytopoiesis indicate that this organ plays a diminishing role in thrombocyte production. During late fetal and early postnatal life the spleen is active in megakaryocytopoiesis. This function is diminished as thrombocyte production is shifted from the spleen to some other organ, probably the bone marrow.A few mitotic megakaryocytes were observed but these are relatively rare. Mitosis was confined to the most immature type of megakaryocyte.Nuclear pleomorphism was in evidence throughout the various age levels but was more noticeable in the early postnatal animals.Phagocytosis by these giant cells could not be confirmed. Some of these cells seemed to contain foreign material but it was not possible to determine if this was from actual phagocytic activity or material impinging upon the cytoplasm.