Age-related changes of male mouse submandibular gland: a morphometric and radioautographic study.

The DNA synthesis and the changes of cell population kinetic of aging male mouse submandibular glands were studied by light and electron microscopic radioautography from embryonic day 19 to 21 months postnatal. At the embryonic day 19, the gland consisted of developing acinar cells (49%), intercalated duct (ICD) (37%), juxta-acinar (JA) (3%) and striated duct (SD) cells (11%). At birth, JA cells increased rapidly to 32%, thereafter decreased gradually. At 1 month of age, granular convoluted tubule cells appeared and increased rapidly in number with age. They reached a maximum at 6 month after birth. Then they appeared to decrease gradually from 6 to 21 months. The most conspicuous feature of the aged submandibular glands was the regressive changes of the granular ducts. The extent and height of the granular ducts as well as the content of mature secretory granules decreased. These changes may play an important role during the development of mice, because the granular duct synthesizes many biological factors. The 3H-thymidine labeling index of each cell type of male mouse submandibular glands reached a peak 1 day after birth and decreased with aging. The labeling index of intercalated duct cells was higher than the others and persisted for a long time. On the other hand, the labeling indices of the other cells were significantly depressed at one week after birth. From these observations on morphology, it was also shown that ICD cells were concerned with the generation of the other cell types.