Intercalated duct cells in the rat parotid gland may behave as tissue stem cells

This study was conducted to determine whether intercalated duct cells in the rat parotid gland have the properties of tissue stem cells. After induction of cellular proliferation by repeated administration of isoproterenol (IPR), a β-adrenergic agonist, proliferation activity in acinar, intralobular, and intercalated ductal cells was quantified using Ki-67 immunohistochemistry. The total number of each type of component cell in a gland was also estimated in the course of IPR treatment. IPR was found to induce proliferation of acinar and intercalated duct cells, but not intralobular duct cells. The total number of acinar cells in a gland on day 5 of IPR treatment was 1.6 times of that at day 0 (baseline). In contrast, the total numbers of intercalated and intralobular duct cells did not change from baseline, indicating a high possibility that the proliferated intercalated duct cells differentiated into acinar cells. On days 2 to 3 of IPR treatment, intercalated duct cells with amylase-positive secretory granules were recognized in a region very close to the acini, and were suspected of being transitional cells from intercalated duct to acinar cells. This quantitative study indicates that intercalated duct cells may have the properties of tissue stem cells upon IPR stimulation.     

Ultrastructural responses of rat exocrine pancreas to cholecystokinin octapeptide and secretin

The study examines the ultrastructural changes in the rat pancreas stimulated in vivo to secrete zymogen and fluid by the hormones cholecystokinin and secretin, administered either separately or in combination. The octapeptide of cholecystokinin (CCK-OP) (2.5 X 10(-7) g/kg) 5 min after injection produced discharge of electron-dense zymogen into the acinar lumen and intercellular canaliculi (ICC), leaving misshapen, collapsed zymogen granule profiles around the lumen. Five minutes after secretin (7.5 clinical units/kg), acinar cells were distended, rough endoplasmic reticulum was dilated, acinar lumina and ICC were expanded and filled by electron-lucent and flocculent contents, and there were "halo" zymogen granules and pale "vacuoles." Electron-lucent zones surrounding acinar and duct cell microvilli indicated transcellular fluid secretion. When secretin was administered with CCK-OP, the picture was a composite between zymogen and fluid secretory patterns. Zymogen granules took up fluid producing a halo appearance, pale vacuoles formed in acinar cells, and acinar lumina and discharging zymogen granules were of intermediate electron density. The results demonstrated that, although fluid is secreted by duct cells in response to secretin, a major site of secretin-stimulated fluid secretion is acinar cells. Fluid is transported across both cell types by transcellular routes, and the acinar cell fluid secretion is integrated with zymogen discharge. CCK-OP produces partial discharge of undiluted zymogen by exocytosis.     

The pathobiology of salivary gland

Summary In the transgenic TG.SH (mouse mammary tumour virus/v-Ha-ras) mouse, designed to develop mammary tumours, occasional spontaneous salivary gland tumours have been reported, predominantly in males. The incidence and histomorphology of salivary gland tumours in 73 TG.SH mice were surveyed and in total, 21.9% developed both overt and microscopic parotid tumours. The majority developed between 73 and 150 days of age. In 31.5% of the TG.SH mice, occasional unilateral, but more frequently bilateral exophthalmos due to hyperplasia of the intraorbital (Harderian) lacrimal gland was observed. In 70% of these animals, parotid tumours developed later. Since Harderian gland hyperplasia, occurring as early as 5 weeks of age, preceded the development of palpable salivary gland lesions, this stigma is useful for the early selection of animals likely to progress to tumour formation. Before tumour-bearing transgenic mice are considered to be suitable models of human neoplastic disease, morphological characterization is necessary to ensure that the tumours are histologically representative of the human lesions for which they are potential models. In this study, all parotid tumours consisted of acinar-like glandular structures with central lumina discernible by electron microscopy. Ultrastructurally, secretory granules evident in the apical cytoplasm of the tumour cells resembled the zymogen granules of the normal parotid acinar cell, and some cells had a prominent complement of rough endoplasmic reticulum. These features, along with focal amylase expression detected immunohistochemically in some parotid tumours, identified these neoplasms as acinic cell carcinomas that mimic the human salivary gland acinic cell carcinoma faithfully.     

Changing myoepithelial cell distribution during regeneration of rat parotid glands

The distribution of the myoepithelial cells during regeneration of the rat parotid gland after atrophy induced by one week of parotid duct ligation was investigated by immunohistochemistry for actin and transmission electron microscopy (TEM). Immunohistochemically, residual ducts were surrounded by actin-positive cells when clips were removed from the duct. Three days later, most of the newly formed acini originating from the residual ducts were also embraced by actin-positive cells. After 10 days, actin-positivity tended to be seen as dots around acini that decreased in number day by day. On day 21 actin-positive cells mainly surrounded intercalated ducts with only a few positive reactions identified at the acinar periphery. Electron microscopically, residual ducts and newly formed acini were peripherally embraced by myoepithelial cells before day 5. After day 7, shift of myoepithelial cells from the periphery of acini to the duct-acinar junctional region was identified. Then few myoepithelial cells were identified at the periphery of acini. These observations indicate that myoepithelial cells migrate from the acinar periphery to the duct-acinar junctional region during rat parotid regeneration, and that such behaviour is closely related to that seen during rat parotid development.     

Cell death and cell proliferation during atrophy of the rat parotid gland induced by duct obstruction

Rat parotid gland atrophy after unilateral duct ligation was studied by light and electron microscopy. Death of secretory acinar cells, which took the form of apoptosis, resulted in their complete disappearance within 5 days. The remnants of the dying cells were mostly phagocytosed and degraded by macrophages within the glandular epithelium; a few were taken up by adjoining epithelial cells. The acinar cell deletion was accompanied by increased mitosis of striated and intercalated duct epithelial cells. However, over many weeks, there was enhanced apoptosis of duct cells, which eventually led to marked shortening of intercalated ducts. Apoptosis of capillary endothelial cells was observed and may account for the reduction in the capillary bed known to accompany gland atrophy. The end-stage lesion comprised small numbers of ducts in a condensed stroma. Compensatory hyperplasia, involving proliferation of duct and acinar cells, was demonstrated in the contralateral glands.     

X-ray microanalysis of the rat parotid gland after chronic sympathectomimetic stimulation

The effects of chronic treatment with isoproterenol, reserpine, prenalterol, and terbutaline on rat parotid gland were investigated by electron microscopy and X-ray microanalysis. Chronic isoproterenol treatment induced lower potassium and calcium concentrations in the acinar cells. The cells were enlarged and contained more and larger zymogen granules than acinar cells in the controls. The zymogen granules contained markedly less sulfur, potassium, and calcium than in control animals. Prenalterol had effects similar to those of isoproterenol, but less pronounced, whereas terbutaline had no significant effects. Chronic treatment with reserpine caused a decrease in calcium levels but did not affect potassium levels. The changes in elemental composition in parotid acinar cells after chronic treatment with isoproterenol and reserpine differed from those induced by the same treatment in the submandibular gland of the rat.     

Distribution of elements in the pancreatic exocrine cells determined by electron probe X-ray microanalysis

We measured the intracellular electrolytes of acinar cells by making electron probe X-ray microanalysis of hydrated and dehydrated sections of freshly frozen dog pancreas.The concentrations of electrolytes in the cytoplasm were: Na 4.8±2.1, K 132±15, Cl 14±4.7, P 165±36, S 19±2.8 and in zymogen granules: Na 6±5, K 60±16, Cl 31±20, P 36±8, S 172±25, Ca 7±5 (mean±S.D. mmol/kg wet weight).The cytoplasm, which is rich in rough endoplasmic reticulum, had low Na and high K concentrations, as compared with levels in the acinar cells of other exocrine glands such as the submandibular gland, the bulk of which is occupied by secretory granules. Though the representative feature of secretory granules was a high S content, occasionally low S peaks of spectra from secretory granules were obtained. These findings may reflect the content of mature zymogen granules and immature condensing vacuoles.Pilocarpine stimulation increased cytoplasmic Na, Cl and Ca and decreased K levels in the pancreatic acinar cells. This indicates that secretory stimulation increases the permeability of the cell membrane to Na, Cl and K ions and that there is a simultaneous Ca release from the intracellular Ca stores such as zymogen granules and endoplasmic reticulum, and/or Ca influx from the extracellular space.     

Filamentous Inclusions in Acinar Cell Carcinoma of the Pancreas

Acinar cell carcinoma of the pancreas exhibits a spectrum of histologic appearances. Some tumors can be readily identified by light microscopy, but others resemble endocrine/neuroen-docrine neoplasms. Ultrastructurally, though large zymogen granules of acinar cells are usually distinctive, the zymogen granules of neoplastic acinar cells are sometimes abnormally small, overlapping in size with the granules of endocrine/neu-roendocrine neoplasms. Six cases of acinar cell carcinoma, two with a typical histologic appearance and four that resembled endocrine/neuroendocrine tumors, were studied ultrastructurally. In addition to zymogen granules and abundant rough endoplasmic reticulum, all cases of acinar cell carcinoma exhibited pleomorphic, membrane bound inclusions that contained filaments. Similar inclusions were not identified in islet cell or carcinoid tumors, and several findings indicate that the inclusions represent deranged zymogen granules. In the ultrastructural study of a pancreatic neoplasm with granules, these inclusions may provide a clue for the diagnosis of acinar cell carcinoma.     

Undifferentiated sarcoma of the parotid gland with osseous metaplasia

Malignant spindle cell tumors of the parotid gland are a diagnostic challenge. We present an unusual case of such a tumor that occurred in the right parotid gland of a 53-year-old man. The clinical and histologic assessments were consistent with a primary sarcoma of the parotid gland. The tumor was composed of sheets of pleomorphic, spindle-shaped cells with an area of bone formation. By immunohistochemistry, the tumor cells were positive for vimentin and negative for epithelial markers. Electron microscopy revealed mesenchymal cells containing moderate amounts of rough endoplasmic reticulum. The major differential diagnostic considerations were spindle cell carcinoma, carcinosarcoma, and primary undifferentiated sarcoma with osseous metaplasia. The lack of epithelial features and the benign appearance of the bone formation led to a diagnosis of undifferentiated sarcoma of the parotid gland.     

Peroxidase activity in the submandibular gland of the house musk shrew, Suncus murinus (Soricidae, Insectivora)

Endogenous peroxidase activity in the submandibular gland of the house musk shrew, Suncus murinus was cytochemically investigated by light and electron microscopy using 3,3'-diaminobenzidine-tetrahydrochloride salt (DAB). The submandibular glands of male Suncus murinus at 8-month-olds were excised and diced into small pieces. In general, salivary glands are structurally divided into a terminal portion comprising a secretory portion and duct system. The submandibular gland of the Suncus murinus, the terminal portions consisted of proximal and distal acinar cells. On the other hand, a granular duct cell of the duct system contained a number of characteristic myelin-like bodies. In the present study, the peroxidase reaction products were localized in the secretory granules of the proximal acinar cells and in the endoplasmic reticulum, Golgi apparatus and myelin-like bodies of the granular duct cells. These reaction products were reduced when 5 mM 3-amino-1,2,4-triazole was added to the reaction medium. Additionally, release of peroxidase into the lumen was observed. In conclusion, the proximal acinar and granular duct cells formed peroxidase and may have performed excretory secretions. Moreover, the peroxidase positive myelin-like body consisted of lamellated membrane and its outer surface membrane continued to the endoplasmic reticulum.     

Formation and fate of ethionine-induced cytoplasmic crystalloids in rat parotid acinar cells

The formation and fate of cytoplasmic crystalloids in rat parotid acinar cells were investigated during ethionine intoxication and recovery. By day 3 of ethionine treatment, acinar cells had numerous autophagic vacuoles containing recognizable secretory granules and fragments of rough endoplasmic reticulum. By day 5, immature crystalloids were present in many of the autophagic vacuoles, and as the crystalloids matured, a 7-nm periodicity became apparent. Crystalloids were never observed in the Golgi saccules or in any other organelle associated with secretory granule formation. When ethionine treatment was stopped, the acinar cells rapidly returned to their normal morphology. The majority of the crystalloids and autophagic vacuoles were lost from the cells during the first two to three days of recovery. At this time annulate lamellae were present intracellularly, and macrophages, many contaning crystalloids, were associated with the basal surface of the acinar cells. These results indicate that the cytoplasmic crystalloids are formed in autophagic vacuoles, and do not represent an abnormal secretory product. Additionally, during recovery crystalloids may be removed from the acinar cells by interaction with macrophages. The sequence of autophagic vacuole formation, development of crystalloids, macrophage infiltration and phagocytosis of acinar cell debris appears to be a non-specific response of the rat parotid gland to cellular injury occurring in a variety of experimental and pathological conditions.     

On the ultrastructure of the parotid and submandibular gland of the mongoose Herpestes edwardsi (Viverridae) (author's transl)

The parotid and submandibular glands of the mongoose are described. Essential differences between the 2 glands were recognized in the acini; however, the intra- and interlobular ducts are built up similarly. The parotid gland is acinar. Its secretory cells are filled with distinct types of granula, which show a considerable variation of size and structure of their secretory material. Organelles are found sparsely. The submandibular gland, however, is tubuloacinar. Its tubuli are capped with cells which belong to the demilunes of v. EBNER, but because of their pale granules they occupy an exceptional position. As the acinar cells of the parotid gland, they form intercellular canaliculi by their plasmalemmata. In the secretory cells of the tubules an intimate contact between the rER and the granules is observed. The intralobular duct surface is built up by an onelayered epithelial cell formation. The cytoplasm of the intercalated duct cells is rich in bundles of filaments, and these cells contain mitochondria with a particular dense matrix. Some microvilli cover the apical surface. In the cells of the striated ducts several populations of granules differing in size and electron density are found. The material of the dense granules shows a marginal plate-like condensation, sometimes it cristallizes. It is supposed that they were released by an apocrine extrusion mechanism. Terminal axons innervate the acini, the duct cells, and also the myoepithelial cells. The findings are compared with the well-known morphology of the salivary glands of the cat.     

Immunocytochemical and morphometric analysis of acinar zymogen granules in human acute pancreatitis

Summary In the present study fine structural changes of acinar zymogen granules were investigated in human acute pancreatitis. Pancreatic tissue was obtained at surgery from 6 patients, prepared for ultrastructural analysis, and stained immunocytochemically for trypsinogen. Stereological parameters of zymogen granules were evaluated. The density of the immunocytochemical labelling for trypsinogen was estimated over zymogen granules, the rough endoplasmic reticulum, Golgi apparatus and the acinar lumina. In acute pancreatitis the number of zymogen granules was diminished and their size reduced. The density of the labelling for trypsinogen was unchanged over zymogen granules but showed a significant reduction over the rough endoplasmic reticulum, Golgi apparatus, and the acinar lumina. In general the integrity of zymogen granules was well preserved. Focally degenerative changes of zymogen granules and large autophagosomes were observed. From the immunogold labelling a disturbance of enzyme synthesis and secretion was suggested. Evidence is given that a disruption of the zymogen granule membranes and a fusion with lysosomal bodies might contribute to the pathogenesis of human acute pancreatitis.     

Radiation-induced damage to lacrimal glands: an ultrastructural study in Sprague Dawley rats

Injury to lacrimal glands represents a major health problem after radiation therapy of the head and neck malignancies. Accordingly, this study aimed to investigate significant ultrastructural changes of lacrimal glands and some of their underlying mechanisms following the exposure to different fractionated doses of irradiation. In this study, 28 Sprague Dawley (SD) rats were assigned to four groups (seven rats each): Group I acted as control and received no irradiation. Groups II–IV received fractionated irradiation of 5 Gy (100 cGy/fraction daily for 5 days), 9 Gy (300 cGy/fraction daily for 3 days), and 20 Gy (one fraction), respectively. One month after the experiment, examination of lacrimal glands with transmission electron microscopy (TEM) demonstrated dose-dependent ultrastructural changes in the lacrimal acinar and intralobular ductal epithelial cells. In the acinar cells, there were swollen rough endoplasmic reticulum, irregularly shaped nuclei with chromatin condensation, mitochondrial damage, and retention of secretory granules. Intaralobular ductal epithelial cells showed loss of surface microvilli and damage to mitochondria. In addition to the potential direct effects of irradiation on lacrimal acinar and intralobular ductal epithelial cells, damage to blood vessels and nerve endings seemed to mediate some of the underlying mechanisms of these irradiation-induced ultrastructural changes. In conclusion, using TEM reveals that lacrimal gland is highly sensitive to even small doses of irradiation therapy; in addition, swelling of rough endoplasmic reticulum and aberrant nuclei are the most encountered structural changes. Damage to blood vessels and nerve endings might mediate some of the underlying mechanisms of irradiation-induced secondary injury in lacrimal glands.     

腮腺主导管结扎诱导萎缩后的组织转归

背景：人体大唾液腺常因受到头颈部肿瘤放射治疗、舍格伦综合征及涎腺炎等因素的影响发生腺体萎缩,目前对长期萎缩性腮腺内组织形态变化的观察仍较少。 目的：观察腮腺主导管结扎诱导腮腺萎缩后的组织转归。 方法：通过结扎SD大鼠右侧腮腺主导管诱导腺体萎缩,采用苏木精-伊红染色观察正常腮腺及导管结扎后0(对照),1,3,7,14,30,60 d萎缩性腮腺组织内腺泡、导管细胞的面积;免疫组织化学染色定量分析肌上皮细胞在腮腺萎缩不同时间点的数量分布变化。 结果与结论：结扎腮腺主导管后腺泡细胞出现快速凋亡,至14 d时已基本消失。随着腺体萎缩,间质逐渐纤维化并伴随炎性细胞浸润,组织内形成大量导管样结构,导管面积逐渐增加,到14 d时达到顶峰,随后逐渐减少,导管样结构呈典型的双套层结构,结扎各时间点腺泡、导管面积与对照组比较差异均有显著性意义(P < 0.05)。结扎后7 d内肌上皮细胞数量快速增加,随后肌上皮细胞数量增长缓慢,维持在一定的范围。表明腮腺主导管结扎诱导腺体萎缩早期腺泡细胞快速消失,出现大量导管样结构,肌上皮反应性增殖,随着腺体的萎缩由导管样结构及肌上皮细胞组成“双套层”结构可能抑制腺体的进一步萎缩。     

Ethionine induced degeneration and regeneration in the rat parotid gland: An electron microscope study

The object of the present study was to establish a model for the study of parotid gland regeneration. Adult female Sprague-Dawley rats were placed for 11 days on a protein-free diet with daily intraperitoneal doses of aqueous DL-ethionine equivalent to 0.5 mg/gm body weight, and returned to a normal diet on day 12. At varying intervals, both during and after intoxication, animals were sacrificed and the parotid glands prepared for study with the transmission electron microscope. Ultrastructural observations indicated that damage was essentially limited to the acinar cells, in which the protein synthetic apparatus was the focus of injury. The rough endoplasmic reticulum displayed atypical configurations, loss of attached ribosomes and membrane fragmentation. In the Golgi region, an atypical structure, a “crystalloid” arose during intoxication. Because of the morphology and apparent formation of the “crystalloid” it was assumed to be an abnormal secretion product. Resumption of a normal diet resulted in the rapid restitution of the normal cytoarchitecture. During the first week of recovery, there was prominent mitotic activity in mature acinar cells. It was concluded that the primary effect of ethionine upon the parotid gland is interference with the function of the protein-synthetic apparatus, leading to morphologic alteration of the acinar cells. The mitotic activity observed during recovery indicated that in the adult rat, acinar cells retain the potential for proliferation.     

Ultrastructural changes in the sheep pancreas stimulated in vivo by secretin, cholecystokinin, and carbachol

An ultrastructural study of the sheep pancreas indicated that secretin, in low dose, stimulated ion and water transport through acinar cells, the evidence including dilatation and vesiculation of rough endoplasmic reticulum, vacuoles, and pale flocculent acinar lumina; that cholecystokinin, in low dose, stimulated incomplete discharge of zymogen from granules producing distorted granule profiles and electron-dense lumina; and that carbachol, in high dose, produced uptake of fluid by acinar cells, evidenced by dilatation of rough endoplasmic reticulum and pale flocculent vacuoles, and discharge of fluid and zymogen by the vacuoles. The ultrastructural findings were consistent with the physiological studies of stimulated pancreatic juice. Secretin induced predominantly fluid secretion, cholecystokinin stimulated viscous juice with a high zymogen concentration, and carbachol produced elevated amylase concentrations with high flow rates. In normal physiological pancreatic secretion, a combined fluid and zymogen secretion by acinar cells would keep the pancreatic juice flowing freely down the acinar tubules. Pancreatic obstruction in cystic fibrosis or chronic alcoholic pancreatitis may arise from excessive degranulation or insufficient water and electrolyte secretion by acinar cells.     

A granular cell at the acinar-intercalated duct junction of the rat submandibular gland

A granular cell was present at the acinar-intercalated duct junction in submandibular gland of adult rats of several different strains. It occurred more frequently in females thanin males. It was a small pyramidalshaped cell, usually forming the most proximal part of the intralobular duct system. The cell contained a relatively large, basally located nucleus. Numerous heterogeneous granules, usually exhibiting both electron-dense and electron-lucent regions, were present in the apical cytoplasm. Exocytosis of the granules at the apical cell surface was occasionally seen. Dilated cisternae of endoplasmic reticulum were frequently observed between the apical granules and in the basal and lateral cytoplasm. The function of the granular cell is unknown. Their structure and location suggest that they may (1) constitute a mature secretory cell population, or (2) represent progenitor cells for acinar and/or intercalated duct cells.