Effects of conditioned medium from bone marrow of normal and Ara-C-treated mice on hemoglobin synthesis.

Differentiation of CFUs toward erythropoiesis has been demonstrated in mice treated with a single dose of Ara-C, and this preferential differentiation was shown to be under the influence of diffusible factors. The aim of the work reported here was to determine whether these factors might include erythropoietin (Ep). This possibility was explored by testing the effect of the Ara-C-induced factor(s) on hemoglobin synthesis, and the effects of anti-mouse Ep on the activity of Ara-C-induced factors. When the late erythropoiesis stage of fetal liver cells was stimulated by bone-marrow-conditioned medium, no significant difference was observed between the effects of conditioned media obtained from normal versus Ara-C-treated bone marrow cells. Bone-marrow-conditioned medium induced a dose-dependent effect on hemoglobin synthesis by fetal liver cells (or adult bone marrow cells); the resulting curve was not parallel to the log-dose-response curve of purified mouse Ep. Anti-mouse Ep inhibited the activity of mouse Ep in fetal erythroblast cultures, but did not affect the stimulatory activity of conditioned media. Below the plateau doses no cumulative erythropoietic effect was observed in fetal erythroblast cultures when conditioned medium was added to Ep. Thus the present data suggest that the effect of bone-marrow-conditioned medium results from at least two independent factors: the first one active on CFUs differentiation towards erythropoiesis, and the second one active at a later stage of erythroid maturation. These factors can be considered to be molecules with an immunogenic structure unrelated to that of Ep.