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Release and restoration of the secretory granules in the convoluted granular tubules of the rat submandibular gland

Morphological changes in the secretory cells of the convoluted granular tubules of the rat submandibular gland were studied following the stimulation of salivary secretion with pilocarpine nitrate. The mechanism of synthesis of secretory protein by these cells is controversial and this study was undertaken to help elucidate this mechanism. It was found that the cells expelled the contents of their secretory granules in the typical exocrine fashion. Shortly after secretion, increased volumes of rough endoplasmic reticulum appeared in the cytoplasm. The endoplasmic reticulum underwent a sequence of morphologic changes and disappeared from the cytoplasm as the secretory products were restored. Additionally, the Golgi complex showed changes. The results of this study indicate that the secretory cells of these tubules follow the accepted exocrine pattern of secretory production and discharge and that they synthesize exportable proteins at a rate far below that of other exocrine systems. The relationship of these findings to the observation that under non‐stimulated conditions the cytoplasm of these cells lacks some of the organelles which are normally associated with exocrine type protein production is discussed.