Localization of Zinc in the Rat Submandibular Gland and the Effect of its Deficiency on Salivary Secretion

Abstract

To clarify the role of zinc in the mechanism of salivary secretion, the effects of zinc deficiency on the morphologic findings and secretory function of the salivary gland were investigated with a rat model of chronic zinc deficiency, prepared by feeding a zinc-deficient diet, and a rat model of acute zinc deficiency, prepared by administration of a zinc chelator, dithizone. In rats with chronic zinc deficiency, the granule production in the granular duct cells was decreased, but the glandular epithelial cells and myoepithelial cells showed no degenerative or other destructive morphologic changes. The degranulation of the granular duct cells and acinar cells in response to acetylcholine hydrochloride seen in control rats was strongly inhibited in rats with acute and chronic zinc deficiency. The contractile response of the actin microfilament bundles in the myoepithelial cells to acetylcholine seen in the control rats was also absent in the zinc-deficient rats. Further, electron microscopy of the submandibular gland stained by Timm's method disclosed prominent zinc localization at the membrane surface, granules, and vesicles of the glandular epithelial cells and in the pits of the myoepithelial cells. These findings suggest that zinc, together with many zinc-dependent enzymes, is closely involved in the production and degranulation of secretory granules in the glandular epithelial cells, and also in the contraction of the myoepithelial cells in the submandibular gland.