Red cell aging in vivo.

Previous studies of red cell structure and metabolism during the aging process have relied upon in vitro techniques of cell separation into various age populations. Probably the most common approach is to isolate the older red cells with the assumption that they are more dense. This may lead to a number of inconsistencies in observations, and may certainly raise questions about possible cell changes secondary to manipulative procedures. For this reason, an experimental system was devised where a normal red cell population could be studied, while aging, in an in vivo environment. The initial red cell mass of a large number of inbred rats was transferred repeatedly into an ever smaller number of animals, making it possible to follow an aging population of red cells up to 48 days while preventing contamination with newly produced cells by suppression of erythropoiesis with transfusion-induced polycythemia. During this period, samples of progressively older red cells could be obtained for measurements of red cell constant. It was noted that the normal rat red cell undergoes both volume reduction and significant hemoglobin content loss with aging. In addition, the hemoglobin concentration within the cell demonstrated an early rise after a return to nearly normal values. These findings are noteworthy in that they help to explain the characteristics of life-spans of cohort labeled red cell populations in small animals, and provide a possible example of a cell's remodeling process within the spleen.