Electron Microscopic Radioautopgraphic Study on Mitochondrial Protein Synthesis in Colonic Epithelial Cells of Aging Mice

For the purpose of studying the aging changes of macromolecular synthesis in the colonic cells of experimental animals, we studied 10 groups of aging mice during aging from fetal day 19 to postnatal month 24. They were injected with 3H-leucine, a precursor for protein synthesis, sacrificed and the colonic tissues were processed for light and electron microscopic radioautography. On many radioautograms the localization of silver grains demonstrating protein synthesis in colonic epithelial cells in respective aging groups were analyzed qualitatively. The results revealed that the number of mitochondria increased from embryonic day 19 to postnatal adult month 1 and 2, reaching the maximum, then decreased to senile year 1 to 2. On the other hand, the number of labeled mitochondria showing protein synthesis increased from embryonic day 19 to postnatal newborn days, adult month 1 and 2, reaching the maximum and decreased to month 24. To the contrary, the labeling index increased from embryonic day 19 to postnatal day 3, reaching the maximum, then decreased to day 14, increased to month 1, decreased to month 6, increased to month 12 and decreased to month 24, indicating the aging changes. These results demonstrated that intramitochondrial protein synthesis in the colonic epithelial cells increased and decreased again and again for 3 times repeatedly due to aging of individual animals depending upon the cellular activities at respective aging stages