The parotid gland of the rat contains high levels of a secretory DNase with a substrate preference for native DNA, requirement for divalent cations (Mg+ +) and pH optimum at 7.5. This enzyme appears not to be found i n the submaxillary-sublingual gland complex, which has only a low level of DNase activity with a contrasting substrate preference for denatured DNA. Neonatal submaxillary and parotid glands both contain a constant, low level of activity which is similar in magnitude to that of the adult submaxillary gland. DNase activity in the neonatal parotid begins to increase between 10-and 15-days post-partum and rises 10,000-fold by 30-days. The substrate preference of the low DNase activity present in the parotid gland prior to ten days was determined for newborn rats, and was found similar to the adult submaxillary rather than to the adult parotid enzyme, since the newborn extract preferentially hydrolyzed denatured DNA. These results support the working hypotheses; that the parotid gland DNase is not found in the other salivary glands and is thus a specific marker of parotid differentiation, and that the synthesis of this enzyme in the parotid gland does not begin until after ten days post-partum.
The results obtained here are discussed in terms of the possible relationships between early tissue interactions i n the embryonic gland rudiments and their later assumption of a cell-specific pattern of protein synthesis, and these relationships are compared to those found in previous analyses of the embryonic pancreas (Rutter et al., '67a). It is suggested that the regulation of specific cytodifferentiation in the salivary glands may be basically different in mechanism than that of the pancreas.
This paper reports investigations in progress on the differentiation of the rat salivary glands. These secretory organs originate as solid buds from the oral epithelium, and, as a consequence of inter-