Growth of replicating DNA chain in adult and old rat spleen

The rate of growth of the DNA chain length was found to decrease in rat spleen with aging. This can be substantiated by the slowing down of transformation of old spleen 3H-labeled DNA with low molecular weight to that with high molecular weight as labeling time increases. At the same time, the intensity of the DNA total synthesis is higher in old spleens than in adult ones. This may result from an increase of mitotic activity in rodent spleen with aging. In its turn, the increased mitotic activity may represent an adaptive reaction responsible for maintaining the number of immunocompetent cells which tend to decrease with aging. The slowing down of the newly formed DNA chain growth may lead to the decreased rate of stabilization of the secondary structure of replicating DNA in old spleen.