Tetsuji Nagata
For the purpose of studying the aging changes of macromolecular syntheses inthe pancreatic acinar cells of experimental animals, we studied 30 groups of agingmice, during aging from fetal day 19 to postnatal month 24. They were injectedwith one of the nucleic acid precursors such as 3H-thymidine for DNA precur-sor, 3H-uridine for RNA precursor or 3H-leucine for protein precursor, then thepancreatic tissues were fixed and processed for light and electron microscopicradioautography. On many radioautograms the localizations of silver grains demon-strating DNA, RNA and protein syntheses in pancreatic acinar cells were analyzedqualitatively and quantitatively.
The number of mitochondria per cell, the number of labeled mitochondria withsilver grains in respective aging groups were counted. The results revealed thatthe nuclei of pancreatic acinar cells, centro-acinar cells, ductal epithelial cells, andendocrine cells were labeled with 3H-thymidine, 3H-uridine or 3H-leucine, demonstrating nucleic acid or protein syntheses. On the other hand, we also found thesilver grains in mitochondria of various cells not only in the nuclei of such cells asthe livers, kidneys or adrenals showing intramitochondrial DNA, RNA and proteinsyntheses. We found that the activities of DNA, RNA and protein syntheses in mi-tochondria of various cells changed due to aging of individual animals. The numberof mitochondria, the number of labeled mitochondria and the mitochondrial labeling index labeled with silver grains were analyzed in each pancreatic acinar cell.It was demonstrated that the numbers of mitochondria, the numbers of labeledmitochondria and the labeling indices in the pancreatic acinar cells showing DNA,RNA and protein syntheses changed due to aging. The DNA synthetic activityincreased from prenatal day 19 to postnatal day 14, then decreased to month 24,the RNA synthetic activity increased from embryonic day 19 to postnatal month 6,then decreased to month 24, while the protein synthetic activity decreased fromprenatal day to postnatal day 1, then increased to postnatal month 2 and decreasedagain to month 24. These results demonstrated the aging changes of mitochondrialmacromolecular syntheses in pancreatic acinar cells of mice.
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