Light microscopic radioautographic study of DNA synthesis in the kidneys of aging mice.

The change of proliferative activity in mouse kidney cortex cells during development and aging was studied by detecting S-phase cells by light microscopic radioautography using 3H-thymidine (3H-TDR). Mouse kidney tissues of various ages: prenatal 13.5, 15.5 and 19.0 days of gestation, postnatal 1 and 8 days, 1 and 2 months, and 1 year were used for this experiment. The kidney cortex tissues were labelled with 3H-TDR either in vitro or in vivo and they were processed for light microscopic radioautography. The labeling indices of the respective cell types were calculated. The labeling indices in glomeruli and uriniferous tubules in the superficial layer were higher than those in the deep layer of metanephric cortex through the developmental stages. However, they decreased rapidly after birth and reached low levels (below 4%) from 1 day to 1 year.