Megakaryocytopoiesis in the mouse: response to varying platelet demand.

The response of murine megakaryocytopoiesis was studied under conditions of varying platelet demand. Twenty-four hours after mice were given a single injection of rabbit anti-platelet serum, megakaryocyte number and volume were increased, becoming maximal at 65 and 40 hr, respectively. Total body megakaryocytic colony-forming unit (CFU-M) numbers did not change until 90 hr, when a 35% increase in the experimental group was noted. The percentage of CFU-M in DNA synthesis in the experimental group was 38 +/-2% at 24 hr, 49 +/- 1% at 40 hr, and returned to normal (11 +/- 3%) at 90 hr. When mice were made thrombocytotic by platelet transfusions, both megakaryocyte number and volume were decreased compared to controls, while no difference was noted in the number and percentage of CFU-M in DNA synthesis. Finally, experiments were performed to examine the effect of platelet transfusions on regenerating marrow. Experimental mice were given platelet transfusions while control animals received platelet buffer solution. At sacrifice the number and volume of megakaryocytes in the experimental group (platelet count 2.568 X 10(6)/microliters) were less than controls (platelet count 0.363 X 10(6)/microliters), while the number and percentage of CFU-M in DNA synthesis were similar in both groups. These results demonstrate that CFU-M are not immediately responsive to acute changes in platelet demand. The data suggest that megakaryocytopoiesis is structured on at least two levels which are independently regulated.