Electron microscopic radioautographic study on mitochondrial rna synthesis in adrenal cells of aging mice

Authors:Tetsuji Nagata
Int J Biol Med Res. 2010; 1(4): 133-143  |  PDF File

Abstract

In order to study the aging changes of intramitochondrial RNA synthesis of mouse adreno-cortical and adreno-medullary 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 adreno-cortical cell, in 3 zones, as well as in each adreno-medullary cell, adrenalin cells and noradrenalin cells, 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 and the labeling index of 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 14, reaching the maxima and decreased gradually from month 1 to month 24. On the other hand, the number of mitochondria in respective 2 types of cells, adrenalin and noradrenalin cells, 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 and the labeling index of 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. Thus, 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 14, reaching the maxima and decreased gradually from month 1 to month 24. In conclusion, it was shown that the activity of intramitochnodrial RNA synthesis in the adreno-cortical cells and adreno-medullary cells in developing and aging mice changed due to aging of individual animals.