DNA SYNTHESIS IN THE PANCREATIC ACINAR CELLS OF AGING MICE AS REVEALED BY ELECTRON MICROSCOPIC RADIOAUTOGRAPHY

For the purpose of studying the aging changes of macromolecular synthesis in animal cells, we studied 10 groups of aging mice during development and aging from fetal day 19 to postnatal month 24. They were injected with H-3-thymidine, a precursor for DNA synthesis, sacrificed and the pancreatic tissues were taken out, fixed and processed for light and electron microscopic radioautography. On many radioautograms the localization of silver grains demonstrating DNA synthesis incorporating 3H-thymidine in the pancreatic acinar cells in respective aging groups were analyzed. The number of silver grains and the number of cell organelles in each cell in respective aging groups were analyzed quantitatively in relation to the aging of animals. The results revealed that the DNA synthesis as expressed by the number of silver grains in cell nuclei, cell organelles, changed with the aging of animals. The number of mitochondria, the number of labeled mitochondria and the mitochondrial labeling index labeled with silver grains were counted in each pancreatic acinar cell. It was demonstrated that the number of mitochondria increased from embryonic day 19 to postnatal newborn day 1, 3, 9, 14, adult month 1, 2 and 6, reaching the maxima, then decreased to senile year 1 to 2.. On the other hand, the number of labeled mitochondria and the labeling indices showing DNA synthesis at various ages increased from embryonic day 19 to postnatal newborn day 1, 3, 9, 14, reaching the maxima and decreased to adult month 1, 2 and 6, to senile year 1 to 2, indicating the aging changes. These results demonstrated that intramitochondrial DNA synthesis in the pancreatic acinar cells increased and decreased due to aging of individual animals depending upon the cellular activities at respective aging stages. Based upon our findings, available literatures on macromolecular synthesis in mitochondria of various cells are reviewed.