Electron Microscopic Radioautographic Study on the Protein Synthesis in the Pancreas of Aging Mice With Special Reference to Mitochondria

The purpose of this study was to investigate the aging changes of macromolecular synthesis in animal cells.We studied 10 groups of mice during development aged from fetal day 19 to postnatal month 24. They were injected with 3H-leucine, a precursor for protein 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 protein synthesis in pancreatic acinar cells in respective aging groups were first analyzed qualitatively. Then 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 number of mitochondria, the number of labeled mitochondria and the mitochondrial labeling index labeled with silver grains were counted in each pancreatic acinar cell.The number of silver grains in cell nuclei and cell organelles changed with the aging of animals. The number of mitochondria, the number of labeled mitochondria and the labeling indices showing protein synthesis at various ages increased from embryonic day 19 to postnatal newborn day 1, 3, 7, 14, to young adult month 1, and 2, reaching the maxima, then decreased at old adult month 6 and senile year 1 to 2, indicating the aging changes.