In vitro and in vivo regulation of hepatic erythropoiesis by erythropoietin and glucocorticoids in the rat fetus.

Glucocorticoids affect evolution of rat fetal liver erythropoietic tissue, where their receptors have been characterized. This paper describes erythropoietin (Ep) and dexamethasone (Dex) effects on the number of CFUE and BFUE grown from erythroid cells isolated from 14 day fetal livers. CFUE number showed a linear log dose-response towards Ep. In absence of exogenous Ep, it was increased by 10(-10) - 10(-9) mol/L Dex. At Ep concentrations less than or equal to 0.025 U/ml, it was increased by Dex concentrations less than or equal to 10(-9) mol/L, higher Dex concentrations being inhibitory. At Ep concentrations greater than 0.025 U/ml, only a linear log dose inhibitory effect of Dex was observed, related to receptor occupancy. BFUE number was not affected by Dex. Ep activity of fetal serum, measured by CFUE induction, was high at 15-16 days of gestation and much lower thereafter. Proliferation of erythropoietic tissue in rat fetal liver before 16 days probably results from high Ep and low corticosterone levels; the regression of proliferation after 16 days probably results from the reverse hormonal status.