The effect of partially purified thrombopoietin on guinea pig megakaryocyte ploidy in vitro.

Enriched populations of guinea pig bone marrow megakaryocytes were prepared by density gradient and velocity centrifugation and maintained in liquid cultures for 24 or 48 h. The resulting megakaryocyte preparations were of 86.1% +/- 5.5% purity. After 24 or 48 h in liquid culture, recovery of viable cells was 77% +/- 11% or 83% +/- 13%, respectively. Megakaryocyte cultures were supplemented with 100-200 micrograms/ml of either a lectin-fractionated preparation of thrombopoietin (TPO) from the plasma of thrombocytopenic rabbits or an identically prepared protein fraction from non-thrombocytopenic animals. Addition of TPO resulted in a significant increase (p less than 0.05) in both the proportion and total numbers of 32N megakaryocytes and a significant decrease (p less than 0.05) in the relative frequency of 8N megakaryocytes. In most experiments, a decrease in the total number of 8N megakaryocytes also was noted. These results indicate that partially purified TPO is able to increase the ploidy (DNA levels) of megakaryocytes in vitro.