Erythropoietin and the inhibitor of erythropoiesis in the amniotic fluid during the first trimester of normal human pregnancy.

The erythropoietic activity of the amniotic fluid from the 1st trimester of pregnancy and of blood plasma of pregnant women was tested biologically on polycythaemic mice by means of radiolabelled 59Fe. It was found that the amniotic fluid exhibits an erythropoietic activity. Then, using Sephadex G-100 gel filtration several fractions of the fluid were separated chromatographically; they were tested on polycythaemic mice for their erythropoiesis-stimulatory and inhibitory activity. It was found that fraction II proteins (mol. w. about 38 000) acted as an erythropoiesis stimulator, while fractions V and VI (mol. w. 6 900 and 4 000, respectively) showed inhibitory properties.