Circulating Megakaryocytes in Blood from the Inferior Vena Cava in Adult Rats

15 male and 15 female rats were investigated for circulating megakaryocytes in the inferior vena cava, using a saponin-haemolysis leucocyte-concentration technique. The number of megakaryocytes per 1.5 ml blood varied from 0 to 10 and was on average 2.5 megakaryocytes per 1.5 ml; there were no significant differences between the two sexes and no correlation between the number of circulating megakaryocytes and the number of platelets. 43 % of the megakaryocytes possessed copious cytoplasm, just under 10 % had sparse cytoplasm, and the remainder were naked nuclei. The shape of the megakaryocytes with cytoplasm was highly variable.