A comparison of mice in rebound-thrombocytosis with platelet-hypertransfused mice for the assay of thrombopoietin.

Rebound-thrombocytosis and platelet hypertransfusions were compared as methods of preparing assay animals for the measurement of thrombopoietin (TSF). In immunothrombocythaemic mice, the amount of 35S incorporation into the platelet mass after injections of a standard dose of TSF was related to the length of time after rabbit anti-mouse platelet serum (RAMPS) injection. After 2 platelet transfusions, however, there was no decrease in 35S incorporation values of mice with time after injections of control or TSF-containing substances. When platelet counts were made 3 days after the last platelet transfusion, the counts decreased with the number of transfusions. Mice in rebound-thrombocytosis were responsive to TSF as evidenced by higher platelet counts (P less than 0.05) and increased 35S incorporation into platelets (P less than 0.005), whereas mice made thrombocytotic by platelet transfusions were not. Assuming that increased platelet counts induced by the different techniques affect assay mice only by inhibiting blood cell production by haematopoietic cells, these data are consistent with the hypothesis that sensitivity to TSF depends upon the proliferative state of the megakaryocytic precursor population.