Hypoxia-induced thrombocytopenia in mice.

In mice hypoxic hypoxia (0.5 atm.) results in a severe and persistent thrombocytopenia with a rapid decline in the platelet count between the fifth and ninth days of hypoxia, after which platelet counts level off at about half their normal value. The thrombocytopenia is not due to the associated polycythemia, splenomegaly, or increased blood volume. There is no significant change in platelet counts of mice made polycythemic by daily injections of 6 units of erythropoietin. Fifteen days of hyperbaria (3 atm.) has no effect on the platelet count of otherwise normal mice. Since there is only a slight decline in platelet count during the first 5 days of hypoxia, the persistent thrombocytopenia appears to be due to either a decreased rate of production of platelets or a structural or metabolic defect in platelets produced under conditions of hypoxia.