Development of exocrine cells of the pancreas and parotid gland in rats. Relation between morphological and biochemical changes.

Electron microphotographs showed that pancreatic acinar cells contain many dense zymogen granules in the fetal stage (day 21 of gestation), both dense and less dense granules in the infant stage (day 10 after birth) and again only dense granules in the adult stage. Injection of dexamethasone in the infant stage greatly increased the number of dense granules, and slightly increased the total number of granules, whereas its injection in the weanling stage (day 24 after birth) did not increase the total number of zymogen granules or their density. Parotid acinar cells contain many zymogen granules of low density in the weanling stage (day 24 after birth), and granules of low density with dense spots in the adult stage. Injection of dexamethasone in the weanling stage increased the number of adult-type zymogen granules, but did not increase the total number of granules. The developmental change in amylase activity was parallel with the change in the high-density areas in zymogen granules, and the latter seemed to be influenced by the serum glucocorticoid level.