Light and electron microscopic radioautographic studies on RNA synthesis in aging mouse adrenal gland

Ultrastructural observation and radioautographic studies were carried out to detect aging changes of RNA synthesis in the adrenal glands of mice from fetal day 19 to postnatal 12 months by light and electron microscopic radioautography after 3H-uridine incorporation. The ultrastructural features of the cells at embryonic stages were not developed. The cell organelles appeared more developed at early postnatal stages. The organelles such as endoplasmic reticulum, ribosomes, Golgi apparatus, mitochondria with tubular or vesicular cristae and lipid droplets were more frequently observed in the cytoplasm of the cells in the 3 zones of the cortex and the medulla at later postnatal and senescent stages. The activity of RNA synthesis of adrenal glands, as expressed by grain counting per unit area as well as per cell, was the highest in the cortex and medulla at fetal day 19, and then gradually decreased with aging. The silver grains were electron microscopically localized over the nucleoli, euchromatin, endoplasmic reticulum, ribosomes and mitochondria of the cells in the 3 zones of the cortex and the medulla. The number of mitochondria per cell, the number of labeled mitochondria per cell and the mitochondrial labeling indices increased along with aging. These results demonstrated the aging changes of RNA synthesis in the adrenal glands of mice.