The regulation of erythropoiesis in the suckling rabbit.

Abstract

Extract: The erythropoietin (ESF) and erythrocyte production after hypoxia and the role of iron in the erythropoietic response to hypoxia were studied in suckling rabbits. There was no spontaneous increase in plasma ESF levels before weaning in spite of a marked “early anemia.” After both bleeding and hypoxia, ESF in plasma rose significantly also during the suckling period. Hypoxia increased total erythrocyte volume (RCV) only slightly in suckling rabbits without iron supplementation. Iron supplementation increased RCV, hematocrit, hemoglobin, and total hemoglobin to levels above normal levels in adult rabbits, which indicates that the regulation of erythropoiesis in this age period is not geared to the same level and is not as accurate as in later life. Factors other than ESF may also participate in the regulation. When hypoxia was induced in iron-supplemented rabbits, RCV per kilogram further increased. The present data indicate that the “early anemia” in rabbits is iron responsive, and that the rate-limiting factor in erythropoiesis in this period is nutritional and not the erythropoietic system of regulation and production. Speculation: Nutritional factors are essential in the development of the “early anemia” in rabbits. Erythropoietin levels are not increased, however, and weight increase is not impaired by the low hemoglobin levels, which suggests that other mechanisms compensate for the “anemia.” In rabbits with essential nutrients in high concentrations, erythropoiesis may, on the other hand, proceed at a rate sufficient to maintain hemoglobin at adult levels even during suckling, thus making compensatory mechanisms unnecessary. This suggests that the “anemia” of the suckling rabbit is physiologic in the sense that adequate amounts of oxygen are transported to the tissues, although it traditionally is considered to be pathologic because it responds to iron supplementation. The “early anemia” illustrates the great potential of the growing organism to function adequately under a wide variety of conditions.