Changes in the main submandibular salivary duct of rabbits resulting from ductal ligation

Normal submandibular ducts from rabbits have been examined by mucosubstance histochemistry, transmission and scanning electron microscopy. The results were compared with the appearances of ducts removed 4...6 weeks after ligation. The normal ducts were composed mainly of columnar "light" cells and basal cells but, in addition, some "dark" cells and scattered goblet containing sulphated mucins were always present. The luminal surface of the ductal cells possessed numerous microvilli protruding into the lumen, and a rim of negatively charged mucin was present on this surface of these cells. After ligation the ducts became greatly distended by their fluid contents which remained under pressure until the duct was incised. The epithelial cells were flattened and appeared to contain less cytoplasm per cell; "light" cells, basal cells and "dark" cells were still recognisable. Goblet cells were much more plentiful than in the control ducts and often protruded into the lumen despite the increased intraluminal pressure. The development of a number of ciliated cells had also occurred and they were often situated close to goblet cells. Lymphatic vessels were more prominent around the ligated ducts. Luminal microvilli were less numerous than in the control ducts but the rim of negatively charged mucin on the luminal surface of ductal cells was more conspicuous. Mixed inflammatory cells were present within the lumina of ligated ducts especially in those parts adjacent to the ductal cells. No inflammatory cell has been observed passing through the wall of a main duct and the possibility exists that these cells had entered lumina within the gland and migrated from there to the main duct. The above findings may serve to help our understanding or physiological events in the ducts.