Secretory Cells of Rat Submandibular Glands

There is a simultaneous increase of both trypsinlike proteolytic activity and the number of granules in the convoluted granular tubules (CGT) of the rat submandibular gland (SMG) during postnatal development.1 Development and maintenance of the CGT granules and proteolytic activity are partially dependent on sex hormones, pituitary secretions, and thyroxine.14 Recently, five trypsinlike enzymes, one of which (glandulain) is testosterone-induced, and another (salivain) which is a major secretary digestive enzyme, have been isolated from homogenates of rat SMGs and purified.5 Because tryptophan is found exclusively in the granules of the CGT, Sreebny and Meyer6 suggest that CGT cells are responsible for the trypsinlike proteolytic activity. However, because the organelles of CGT cells are not arranged in a pattern similar to patterns of other exocrine cells,7-10 protein in the granules may be synthesized elsewhere or by an uncommon mechanism.6 This possibility was recognized by early investigators who found that the CGT, in contrast to other parenchymal cells of the body, accumulated more label at 24 and 36 hours than at 4 hours after injection of 35S-methionine."1