Hematopoiesis and aging: IV. Mass and distribution of erythroid marrow in aged mice.

Aged mice are "anemic," i.e., they have a lower hematocrit than young adult mice, but this appears to be a "dilutional" anemia; the red cell mass is normal. Other observations have supported the hypothesis that basal erythropoiesis does not change as mice grow old. In the present study, the percentage of injected 59Fe found in the skeleton and spleen, 59Fe distribution between various bones and bone groups, and the number of nucleated erythroid cells per humerus were studied and the total mass of erythroid precursors was calculated. There was no significant difference in any of these values between mice aged 3-27 months. The variability of 59Fe distribution within various skeletal parts was no greater in aged than in young mice. Thus, these data further strengthen the case for normal basal rates of erythropoiesis in aged mice.