Inhibition by dexamethasone of erythropoietin-induced amplification of the erythropoietin-responsive cell compartment.

Erythropoietin-responsive cells (ERC) were reduced to very low levels in post-hypoxic polycythemic mice by intraperitoneal injection of 60 mg/kg-mouse of busulfan. Repeated injections of 5 units erythropoietin (Ep), 1, 2, and 3 days after busulfan repopulated the ERC compartment. Therefore, injection of a small test dose of Ep on day 5 induced a considerable wave of erythropoiesis. When busulfan-treated polycythemic mice received 5 mg of dexamethasone together with Ep injections they responded to the test dose of Ep with very minor increases in iron incorporation, which would indicate that a very small increase in the ERC population induced by Ep took place. These results suggest that the inhibitory action of dexamethasone on erythropoiesis is exerted not only by inhibiting the Ep-induced differentiation of ERC into proerythroblasts, but also by inhibiting the effect of the hormone on the amplification of the ERC compartment.