Abstract
Transfusion of platelet concentrates was used to establish a thrombocytosis of approximately three times normal platelet levels in male rats. This thrombocytosis resulted in a rebound thrombocytopenia to 60% of normal counts. Examination of the small acetylcholinesterase (ACh-E) positive cells of the marrow at this time showed a reduction to 50% of normal levels without significant changes in control animals. A second group of experiments indicated that this suppression developed as early as the third day posttransfusion, persisted until day 7, and returned to baseline levels by day 9. Incorporation of 75SeM indicated that the reduction in platelet count was due to decreased platelet production. Little or no changes were observed in the hematocrit or WBC. This evidence supports the hypothesis that these cells are early cells in the megakaryocytic series. They are the earliest cells of the series seen to be affected by thrombocytosis. Feedback control by platelets or platelet extracts of this cell population may represent one level of regulation of megakaryopoiesis.
