Effects of shortened erythropoietin exposure on sheep marrow cultures.

To determine whether erythropoietin (Ep) is required only to trigger, or also to sustain the growth of erythroid progenitor (CFU-E) in vitro, the effect of limiting the time of exposure of sheep bone marrow CFU-E to Ep on erythroid colony (EC) formation was examined. Restricting the in vitro exposure of CFU-E to 2-24 h, either by brief preincubation with Ep or by neutralization of Ep present in culture with anti-Ep, resulted in a 70-90% reduction of EC formation, and the colonies that were produced were of a small size. In contrast, no inhibition of EC size or number occurred when CFU-E were exposed to EP for more than 24 h. These results suggest that Ep also modulates the proliferative events subsequent to the initial triggering of CFU-E which lead to the formation of erythrocytes.