Development of the rat salivary glands: IV. Amylase and ribonuclease activity during embryonic and neonatal development of the parotid and submaxillary glands

Abstract

Amylase and ribonuclease activity were measured in the parotid and submaxillary glands of the rat over the course of their development in vivo. In the parotid, amylase specific activity increases from almost undetectable levels in the 16-day embryonic rudiment, to a fivefold higher plateau between 18 days and birth, and then increases to an adult level which is 5000-fold higher. RNAase activity increases eightfold from 15 days postconception to 7 days postpartum and then begins a more rapid increase to a 20-fold higher adult level. In the embryonic submaxillary gland, both enzymes increase more than 15-fold to reach maximal levels in the few days following birth. In the course of postnatal development, these activities are lost, and in the adult have decreased to the low levels that had been present in the early embryonic rudiments. Measurements of RNAase and amylase activity in a nonsalivary epithelium, the lung, also showed an embryonic increase in enzyme activity. Therefore, attributing the embryonic increases in the salivary enzymes to cell-specific mechanisms is speculative, and the evaluation of their developmental significance depends on the qualitative identification of the different enzyme proteins.