Platelet Production in Hypoxic and RBC‐Transfused Mice

Platelet production rates were studied in hypoxic, red blood cell (RBC) transfused, and normal mice. In addition, platelet depletion was induced in some of the mice by injection of rabbit anti-mouse platelet serum (RAMPS) to stimulate platelet production. Hypoxia alone caused an increase in haematocrit and platelet count at 1–3 d, followed by a decrease in platelet counts to below normal values at 6–7 d. On the other hand, RBC transfusion caused increased haematocrit and decreased platelet count of mice at 1–4 d, with a return of platelet counts to normal by 5–6 d. Normal mice and mice transfused with RBC responded to platelet depletion with rebound-thrombocytosis with maximum platelet production 3–5 d later and elevated platelet counts on days 5–6. However, platelet production in platelet-depleted mice exposed to hypoxia was less marked, and platelet counts did not reach normal levels. The data are consistent with the hypothesis that hypoxia causes thrombocytopenia by stem cell competition between erythroid and megakaryocytic cell lines and/or inhibition of thrombopoietin production.