Changes in erythropoietic activity of the rat plasma in the course of posttransfusion polycythaemia.

The aim of this study was to determine the erythropoietic activity of the plasma of polycythaemic rats and of one of its protein fractions playing a role in erythropoiesis regulation. The erythropoietin activity and that of the erythropoiesis inhibitor varied in the examined plasma samples at definite time periods after induction of polycythaemia. It was demonstrated that the most suitable time of plasma collection for the inhibitor investigation is the period between 115 and 187 h after the first transfusion, and that in some cases separation of this factor from erythropoietin present simultaneously in the plasma is indispensable in order to reveal the inhibitory activity. The erythropoiesis inhibitor administered jointly with erythropoietin was found to exert no influence on erythropoiesis either in normal or in polycythaemic recipients of the tested plasma.