Erythropoiesis. II. Assay of Erythropoietin in Hypophysectomized Rats. ∗

Abstract

Summary and Conclusions

Using incorporation of Fe⁵⁹ into newly-formed red cells as index of red cell production, it has been shown that erythropoiesis is gradually reduced, reaching a minimum in rats at 8 to 13 days after hypophysectomy. A factor of 10 exists between incorporation of Fe⁵⁹ into red cells of normal control (37 ± 4) and the hypophysectomized rat (4 ± 2) at this interval. We have also found that the hypophysectomized rat is an extremely sensitive preparation for assay of factor(s) in anemic plasma that stimulates or mediates erythropoiesis. Our observations may be summarized as follows: 1. Administration of anemic plasma to hypophysectomized assay animal increases incorporation of Fe⁵⁹ 3- to 7-fold. 2. Plasma from hypophysectomized animals and un-operated controls made anemic by repeated phlebotomy increases Fe⁵⁹ red cell incorporation to the same extent when administered to the hypophysectomized assay animal. 3. A single injection of 2 ml of anemic plasma to the hypophysectomized assay animal elicits a 2- to 3-fold increase in Fe⁵⁹ incorporation. The mechanism of rapid reduction of erythropoiesis that follows hypophysectomy in rats and its relationship to increased sensitivity of the hypophysectomized animal to anemic plasma are discussed briefly.