Erythropoietic response of hypertransfused neonatal rats suckled by anemic mothers

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Abstract
Twelve‐day‐old hypertransfused neonatal rats nursed for four days by a twice‐bled mother exhibited higher 48‐hour RBC‐59Fe incorporation than control neonates nursed by a normal mother. Erythropoietin (Ep) in plasma of 12‐day‐old hypertransfused neonates suckled for four days by twice‐bled mothers was initially equivalent to approximately 0.5 IU/day. This calculation was based on the observation that reticulocytosis induced in these animals was similar to that produced in neonates of the same age injected intra‐peritoneally with 0.5 IU Ep for four days while nursing from normal mothers. The reticulocyte maturation curve was shifted to the left in 12‐day‐old hy‐pertransfused neonates suckled by anemic mothers, and in 12‐day‐old normal neonates rendered anemic by bleeding, while nursing from normal mothers. This left‐shift of the reticulocyte maturation curve was also evident in 12‐day‐old hypertrans fused neonates injected with Ep. Decreases in relative percentages of nucleated RBC was evident in spleens of 12‐day‐old neonates nursed by anemic mothers and spleens of 12‐day‐olds injected with Ep. Significant reduction in nucleated RBC were noted in both spleen and marrow of 12‐day‐old anemic neonates. These results suggest: (1) Ep, present in increased amounts in the anemic mother, is transmitted through milk to nursing neonates thereby stimulating erythropoiesis in these animals; (2) Ep may not stimulate stem cell differentiation towards the erythroid compartment but rather acts on already differentiated erythroid cells by influencing their rate of maturation.