Splenic erythropoiesis in rats under hypoxic and post-hypoxic conditions.

In rats chronic hypoxia causes extramedullary haematopoiesis mainly localized in the spleen. It is not known how splenic erythropoiesis develops and how it regresses after termination of hypoxia. In this study the spleen of rats exposed to chronic hypoxia was studied by light and electron microscopy; the findings were compared to relevant peripheral blood values. Splenic erythropoiesis begins almost immediately after exposure to hypoxia and reaches its maximum after 2-4 weeks. It occurs mainly in the splenic cords drawing upon local erythroblasts and is accompanied by an increase in splenic weight as well as a decrease in splenic iron stores. After termination of hypoxia marked phagocytosis by splenic cord macrophages diminishes the number of erythroblasts and of erythrocytes with a concomitant increase in splenic iron stores. Thus, splenic erythropoiesis appears to be inhibited as part of a rebound phenomenon and returned to normal by phagocytosis of erythroid cells within 4 weeks after cessation of the hypoxic stimulus.