Physiological anemia of early development in the rat: characterization of the iron-responsive component.

The purpose of this study was to determine the circumstances under which the postnatal decline in concentration of hemoglobin in the rat can be modified by administration of iron. Base-line dietary regimens contained iron in what is considered an optimal amount, and additional iron-dextran administration to the dams had no significant influence on the concentration of hemoglobin in the pups. However additional iron when administered directly to the pups in the form of iron-dextran or heat-treated red cells did elevate the concentration of hemoglobin. The administration of iron was effective only before weaning at 21 days of age; subsequently, there was no significant effect. The age-related difference in hemoglobin-responsiveness corresponded to the effects of iron treatment on the concentration of serum iron. Between 11 and 21 days of age, serum iron values under base-line dietary conditions were low but they became increased in response to iron treatment. After 21 days of age, base-line serum iron values rose abruptly and were no longer substantially augmented by iron treatment. The findings suggest that a physiological period of low serum iron restricts the production of hemoglobin. During this period, administration of iron in greater than physiological doses was effective in raising the serum iron and the concentration of hemoglobin.