The effects of thrombopoietin on megakaryocyte-cfc, megakaryocytes, and thrombopoiesis: with studies of ploidy and platelet size.

The effects of partially purified thrombopoietin (TPO). prepared from the plasma of thrombocytopenic rabbits, upon megakaryocyte colony-forming cells (Meg-CFC), megakaryocytes, and platelets were evaluated. The thrombopoiesis-stimulating activity of both types of preparations of TPO used was established by their ability to increase the levels of selenomethionine-75Se (75SeM) in the circulating platelets of mice, as described previously. TPO did not increase the frequency or total numbers of Meg-CFC or granulocyte-macrophage-CFC (GM-CFC) in the bone marrow or spleen of recipient mice. Similarly, the addition of TPO directly to 0.3% agar cultures of bone marrow or splenic cells did not alter the frequency of either Meg-CFC or GM-CFC, although in some experiments. concentrations greater than required to stimulate thrombopoiesis in vivo were used. TPO did not enhance the ability of suboptimal concentrations of spleen conditioned medium to support colony growth. Human erythropoietin (EPO) at concentrations from 0.6 U/mI to 8 U/mI, in vitro, did not increase the frequency of bone marrow or splenic Meg-CFC or GM-CFC. As previously reported, two types of megakaryocyte