Electron Microscopic Radioautographic Study on Mitochondrial Rna Synthesis in Adrenocortical Cells of Aging Mice

In order to study the aging changes of intramitochondrial RNA synthesis of mouse adrenocortical cells, 10 groups of developing and aging mice, each consisting of 3 individuals, total 30, from fetal day 19 to postnatal newborn at day 1, 3, 9, 14, adult at month 1, 2, 6 and senescent animals at month 12 (year 1) and 24 (year 2) were injected with 3H-uridine, an RNA precursor, sacrificed 1 hr later and the adrenal tissues were fixed and processed for electron microscopic radioautography. On electron microscopic radioautograms obtained from each animal, the number of mitochondria per cell, the number of labeled mitochondria with 3H-uridine showing RNA synthesis per cell and the mitochondrial labeling index in each adrenocortical cells, in 3 zones, were counted and the results in respective aging groups were compared with each others. From the results, it was demonstrated that the number of mitochondria per cell in 3 zones, the zona glomerulosa, fasciculata and reticularis of respective mice at various ages increased from fetal day 19 to postnatal month 1 reaching the plateau from month 1 to 24 due to development and aging of animals, respectively, while the number of labeled mitochondria per cell with intramitochondrial RNA synthesis incorporating 3H-uridine increased from fetal day 19 to postnatal month 2, reaching the maxima and decreased slightly from month 6 to month 24. The mitochondrial labeling index calculated from the numbers of mitochondria per cell and the numbers of labeled mitochondria increased from fetal day 19 to postnatal day 3, 9 and 14, reaching the maximum and decreased gradually from month 1 and again increased at month 2 and decreased to month 24. It was shown that the activity of intramitochnodrial RNA synthesis in the adrenocortical cells in developing and aging mice changed due to aging of individual animals.