Erythropoiesis inhibiting factor(s) (EIF). The specificity and toxicity of urinary EIF studied in vivo and in vitro.

The specificity and toxicity of the urinary erythropoiesis inhibiting factor (EIF) has been tested both in vivo and in vitro. When EIF was given to ESF stimulated erythropoietically suppressed polycythaemic mice and to mice at maximal endogenous erythropoietic stimulation, a reduction of the erythroid bone marrow cells, the erythropoietic 3H-TdR L.I. and the total number of bone marrow cells were observed. No effect was seen on the myelopoietic bone marrow cells. An unspecific toxic effect was unlikely, since addition of EIF did not alter the proliferation of lymphoblastic cells nor change the glucose utilization of bone marrow cells in vitro. Neither did the amount of dead bone marrow cells increase after being incubated with EIF for 72 h. The results indicate that the urinary EIF is a non-toxic, cell specific inhibitor on erythropoiesis.