Hypoxia increases erythropoiesis and decreases thrombocytopoiesis in mice: a comparison of two mouse strains

Several previous studies have shown that hypoxia increases erythropoiesis and decreases thrombocytopoiesis in mice. It has been postulated that the thrombocytopenia is caused by stem cell competition between the erythrocytic and megakaryocytic cell lines. In the present work, we compared the effects of severe hypoxia (5.5-6.0% O2) in both male and female C3H and BALB/c mice by measuring their abilities to produce red blood cells and platelets. All mice had significant increases in packed cell volumes and marked decreases in platelet production after hypoxia; however, there were significant differences in the degree of stimulation in the two mouse strains. After 14 days of hypoxia, the percentage of 35S incorporation into platelets, total circulating platelet counts and total circulating platelet masses were lower in C3H mice than in BALB/c mice, but platelet sizes were larger. Also, hypoxia caused greater changes in male mice than in female mice, with male C3H mice showing the greatest increase in packed cell volumes and the lowest platelet counts of all mice tested. The least responses were observed in female BALB/c mice. BALB/c mice had higher P50 (right-shifted O2 dissociation curves) and lower erythrocyte 2,3-diphosphoglycerate values than C3H mice, indicating a lower hemoglobin O2 affinity for BALB/c mice. The results indicate that the effects of hypoxia are not direct upon platelet production, but that the thrombocytopenia is a result of stimulation of erythropoiesis. These data support the stem cell competition hypothesis and illustrate that the degree of the inverse relationship between red blood cells and platelet production of hypoxic mice is dependent, to a large degree, upon the sex and strain of mice that are used.