Study of RNA synthesis in the livers of aging mice by means of electron microscopic radioautography.

The application of 3H-uridine radioautography results in labeling of the liver cells in which RNA is synthesized at various ages of the mouse. Quantitative changes of RNA synthesis in the hepatocytes of aging mice were studied by electron microscopic radioautography. The silver grains were mainly located in the nucleoli and nuclei and a few in the mitochondria and rough surfaced endoplasmic reticulum of almost all of the cell populations at various ages. The number of silver grains in the hepatocyte gradually increased after birth, reached the maximum at 14 days of postnatal age, then decreased to 24 months with aging. The number of silver grains of the euchromatin was more than those of the heterochromatin of the hepatocyte nuclei at various ages. The number of silver grains of the granular components was more than those of the fibrillar components of the hepatocyte nucleoli at various ages. However, the ratio of silver grains among euchromatin, heterochromatin, granular components and fibrillar components remained approximately constant.