Effects of thrombopoietin on the number and diameter of marrow megakaryocytes of mice.

A thrombocytopoiesis-stimulating factor (TSF or thrombopoietin) from kidney cell culture medium was injected into mice, and the number and size of megakaryocytes in the bone marrow were determined. For controls, other mice were injected with saline, normal rabbit serum (NRS), or rabbit anti-mouse platelet serum (RAMPS). Both TSF and RAMPS caused significant (P less than 0.0005) increases in the number and diameter of marrow megakaryocytes 2-3 days later. Increases in average megakaryocyte number per high-powered field ranged from 30-191%, while increases in average megakaryocyte diameter in the same mice ranged from 17-45%. After applying the multiple counting correction factor, increases of 6-100% in the number of megakaryocytes were observed. Although the mice injected with RAMPS, to make them thrombocytopenic, showed greater increases in marrow megakaryocyte numbers and sizes than mice injected with TSF, the results demonstrate that TSF from kidney cell cultures stimulated megakaryocytopoiesis.