The regenerating liver: a site of erythropoiesis in the adult Long-Evans rat.

Erythropoiesis, which is primarily hepatic in the rat during fetal and early neonatal life, shifts almost entirely to the bone marrow in the neonatal-adolescent stage of development. In the adult, extramedullary erythropoiesis has been demonstrated in the liver and spleen under certain pathological conditions when bone marrow red cell production is insufficient. In the present study, erythropoietic foci have been found in young-adult rat liver regenerating 24-72 hr after subtotal hepatectomy. This erythropoiesis is both extravascular and sinusoidal, with some erythroblastic islands noted. The centrolobular hepatic area contains the highest concentration of erythroblasts. Peripheral blood reticulocytosis coincides with the appearance of these cells and this is considered as an indicator of effective erythropoiesis. Liver regenerating after partial hepatectomy produces significant quantities of erythropoietin (Ep) in response to hypoxia. Subtotal hepatectomy may confer upon the adult liver the ability to revert to a fetal-like condition both in its ability to produce Ep and to function as a hematopoietic inductive microenvironment for erythropoiesis.