The presence of mast cell granules in rat parotid secretory granule preparations.

Rat parotid secretory granule preparations contain, in addition to the acinar secretory granules, a second type of granule. Whereas the acinar granules lyse under hypotonic conditions, this second type of granule does not, thus providing a means for obtaining a fraction sufficiently enriched in these granules to allow for their characterization. In the present study, these granules are shown to possess demonstrable chymotrypsin-like enzyme activity. In the intact rat parotid, such activity is shown by histochemical methods to be present in the numerous mast cells residing in the connective tissue stroma, but no such activity exists in any of the parenchymal cells. On the basis of their electron microscopic appearance, enzyme activity, and physical characteristics it is concluded that the second type of granule present in rat parotid secretory granule preparations originates from stromal mast cells rather than from parenchymal cells.