Normal ultrastructure and histochemical characteristics of canine lacrimal glands

Lacrimal glands of 12 dogs free of ocular disease were examined to determine the normal structure of these glands. The glands consisted of tubuloacinar cells that ultrastructurally and histochemically were of a single type of secretory cell in the tubules and possibly 3 types of secretory cells in the acini. The tubular epithelium contained homogenous electron-dense granules that stained as neutral glycoconjugates (periodic acid-Schiff positive and Alcian blue and high iron diamine negative). The predominant acinar cells contained granules of lesser electron density than those of the tubules, and stained as sialomucin (Alcian blue [pH 2.5] and periodic acid-Schiff-positive, and high iron diamine-negative). A second type of acinar cell was in peripheral lobules that ultrastructurally and histochemically appeared like lipid granules (positive with oil red O and osmium tetroxide). Ultrastructurally, a third type of acinar granule was finely granular, electron-lucent, and frequently coalesced. It was not readily apparent whether the latter was an artifact, a stage in the maturation of the sialomucin granules, or a third type of acinar granule. Individual acinar cells usually had a predominance of 1 granule type, but greater than 1 granule type could be found in some cells. The basal surfaces of the acinar, tubular, and ductal cells were incompletely ensheathed by myoepithelial cells. Plasma cells, lymphocytes, mast cells, endothelial cells, fat cells, and Schwann cells composed the cellular elements of the interstitium. Lymphocytes, mast cells, and nerve endings also were found in the parenchyma.