Thrombin-stimulated effects on megakaryocytopoiesis and pulmonary-platelet interactions.

The effects of thrombin stimulation on megakaryocytopoiesis and pulmonary-platelet interactions were investigated before and after administration of the compound to 15 mongrel dogs. Each dog served as its own control. Thrombin was given to encourage the traffic of megakaryocytes into the lung and to study the thrombin-stimulated effects on megakaryocytopoiesis in the bone marrow. Our results showed that thrombin increased the numbers of bone marrow cells in general and megakaryocytes (MK) in particular. In addition, the maturation cycle of megakaryocytes was accelerated and the number of MK migrating into the central venous circulation was nearly doubled. Most of the circulating MK ultimately became sequestered in pulmonary capillaries, where platelets were shed into the arterial circulation. We conclude that thrombin has a major stimulatory effect on megakaryocytopoiesis in the bone marrow and that the lung plays an important role as a vascular filter and regulator of circulating platelet count.