Supporting effects of myoepithelial cells in submandibular glands of dogs when acting against increased intraluminal pressure

Physiology, Pathology and Regeneration of Salivary Glands

Salivary glands are essential structures in the oral cavity. A variety of diseases, such as cancer, autoimmune diseases, infections and physical traumas, can alter the functionality of these glands, greatly impacting the quality of life of patients. To date, no definitive therapeutic approach can compensate the impairment of salivary glands, and treatment are purely symptomatic. Understanding the cellular and molecular control of salivary glands function is, therefore, highly relevant for therapeutic purposes. In this review, we provide a starting platform for future studies in basic biology and clinical research, reporting classical ideas on salivary gland physiology and recently developed technology to guide regeneration, reconstruction and substitution of the functional organs.

Parasympathetic control of airway submucosal glands: central reflexes and the airway intrinsic nervous system

Airway submucosal glands produce the mucus that lines the upper airways to protect them against insults. This review summarizes evidence for two forms of gland secretion, and hypothesizes that each is mediated by different but partially overlapping neural pathways. Airway innate defense comprises low level gland secretion, mucociliary clearance and surveillance by airway-resident phagocytes to keep the airways sterile in spite of nearly continuous inhalation of low levels of pathogens. Gland secretion serving innate defense is hypothesized to be under the control of intrinsic (peripheral) airway neurons and local reflexes, and these may depend disproportionately on non-cholinergic mechanisms, with most secretion being produced by VIP and tachykinins. In the genetic disease cystic fibrosis, airway glands no longer secrete in response to VIP alone and fail to show the synergy between VIP, tachykinins and ACh that is observed in normal glands. The consequent crippling of the submucosal gland contribution to innate defense may be one reason that cystic fibrosis airways are infected by mucus-resident bacteria and fungi that are routinely cleared from normal airways. By contrast, the acute (emergency) airway defense reflex is centrally mediated by vagal pathways, is primarily cholinergic, and stimulates copious volumes of gland mucus in response to acute, intense challenges to the airways, such as those produced by very vigorous exercise or aspiration of foreign material. In cystic fibrosis, the acute airway defense reflex can still stimulate the glands to secrete large amounts of mucus, although its properties are altered. Importantly, treatments that recruit components of the acute reflex, such as inhalation of hypertonic saline, are beneficial in treating cystic fibrosis airway disease. The situation for recipients of lung transplants is the reverse; transplanted airways retain the airway intrinsic nervous system but lose centrally mediated reflexes. The consequences of this for gland secretion and airway defense are poorly understood, but it is possible that interventions to modify submucosal gland secretion in transplanted lungs might have therapeutic consequences.

Sialographic images of pathological changes in the mouse parotid gland

In order to correlate pathological changes of mouse parotid glands with their sialographic images, we conducted studies on mice with known pathological changes: mice with Stensen's duct ligated, NZB mice with a systemic auto-immune disease, and aged mice. The sialographic images were found to be specific for the pathological changes: The glands after ligation of Stensen's duct were characterized by dilated, large excretory ducts with a reduced system of peripheral ducts; the glands of NZB mice showed lobular leakage of the contrast medium from small excretory ducts; and the glands of aged mice showed a great reduction in the ductal system. It is concluded that sialography yields useful information on the pathological changes of the ductal systems in the mouse parotid gland.

Nerve interactions in salivary glands

In the salivary reflex, not only secretory cells are activated, but also myo-epithelial cells are contracted to support these cells and promote the flow of saliva, and blood vessels dilate to meet the increased demands of the tissues. The various effector cells often receive nerves from both parts of the autonomic system, and interactions may occur when the nerves act on the same type of effector, or on different types of effectors. While in an experiment electrical stimulation of the sympathetic trunk may decrease a parasympathetic salivary flow by causing marked vasoconstriction, this does not occur in the salivary reflex, since the vasoconstrictors do not take part. On the contrary, the normal sympathetic vasoconstrictor tone of the resting gland is easily overcome by activity in parasympathetic vasodilator nerves when secretion starts. Pronounced synergism can be demonstrated between sympathetic and parasympathetic secretory nerves. In dogs, for instance, in which sympathetic secretion is beta-adrenoceptor-mediated, this is marked in the case of fluid secretion. In rats and rabbits, in which beta-receptors elicit secretion of amylase, the potentiating interaction among the nerves is striking when amylase secretion is considered. Even the random release of acetylcholine from the post-ganglionic parasympathetic axons, by itself insufficient to evoke secretion, can increase the sympathetic effects. Motor nerves interact with secretory nerves by causing myo-epithelial contraction, mechanically promoting secretion. Interactions between the nerves in their long-term regulatory function on the sensitivity of the acinar secretory and myo-epithelial cells can also be demonstrated.

Experimental sialography: the effects of retrograde infusion of radiographic contrast media on salivary gland morphology and function. A review article

An experimental model for sialography, involving retrograde infusion of contrast medium into the rat submandibular gland under continuous pressure monitoring, was developed. Morphologic alterations induced during infusion of water- and lipid-soluble radiographic contrast media and the distribution of the media were examined with light and electron microscopy. An uneven distribution of the media throughout the tissue and variations in the degree of the alterations in different parts of the gland were seen at all stages of filling. The changes primarily consisted of dilation of the luminal system, which successively became more pronounced as infusion continued. Infusion of the lipid-based medium consistently resulted in more severe alterations, including changes in the acini. Tracer studies showed that the water-soluble medium leaked out through the intercellular spaces and to the surrounding tissue, whereas the lipid-based medium appeared to be confined to the luminal space. Ductal filling with either medium resulted in a relatively fast recovery; after prolonged infusion, recovery was slower and additional alterations occurred. The acini showed confluence of secretory granules and vacuole formation. After infusion of the lipid-based compound, autophagic vacuoles and granulomatous alterations developed. Prolonged infusion with either medium resulted in atrophy of the parenchyma and connective tissue proliferation in some glands. An inflammatory infiltrate was present in all glands during the recovery period. Functional alterations, primarily consisting of a decrease in flow rate, were noted after prolonged infusion. The increase in intraluminal pressure induced during infusion was most likely the primary cause of the alterations. In addition, the presence of contrast medium contributed to the long-term effects of the procedure.

A modification of the tannic acid-phosphomolybdic acid-dye stain for demonstrating myoepithelial cells in formalin fixed tissue

A modified tannic acid-phosphomolybdic acid-dye procedure is used for staining myoepithelial cells in formalin fixed surgical and autopsy material. Paraffin sections are brought to water, mordanted for 1 hr in Bouin's fixative previously heated to 56 C, cooled while still in Bouin's, rinsed in tap water until sections are colorless, rinsed in distilled water, treated with 5% aqueous tannic acid 5-20 min, rinsed in distilled water 30 sec or less, treated with 1% aqueous phosphomolybdic acid 10-15 min, rinsed 30 sec in distilled water, rinsed in methanol, stained 1 hr in a saturated solution of amido black or phloxine B in 9:1 methanol:acetic acid, rinsed in 9:1 methanol:acetic acid, dehydrated, cleared and mounted. Myoepithelial cells of sweat, lacrimal, salivary, bronchial, and mammary glands are blue-green with amido black or pink with phloxine B. Fine processes of myoepithelial cells are well delineated. Background staining is minimal and the procedure is highly reproducible.

Saliva secretion from the rat submandibular gland after retrograde infusion of radiographic contrast media

Rat submandibular saliva was collected at various times after retrograde infusion of water-soluble (Renografin 60%) or lipid-soluble (Lipiodol UF) radiographic contrast medium. Significant alterations in flow rate occurred following heavy parenchymal filling with both types of contrast media. Occasional changes in protein concentration, lactoperoxidase activity, and K+ levels were also noted. These changes were relatively mild and transient, and gland function had generally returned to normal by one wk after infusion. No alterations in glandular function were detected after infusion of contrast medium to a degree (ductal filling) comparable to that usually employed in clinical sialography.

A morphologic study of the recovery of the rat submandibular gland after retrograde infusion. I. Water-soluble radiographic contrast medium

The recovery of the rat submandibular gland after retrograde infusion of water-soluble radiographic contrast medium was studied using an experimental model. During continuous monitoring of the developing intraglandular pressure, the glands were subjected to ductal and slight parenchymal filling or heavy parenchymal filling with the medium. The animals were killed after varying recovery periods, and the tissue was prepared for light and electron microscopic examination. Dilation of the ductal lumina, induced during ductal and slight parenchymal filling, was successively reduced and, generally, the parenchyma had a normal appearance at 30 h. In glands subjected to heavy parenchymal filling, the changes in the intralobular ducts were more pronounced and were also seen at later times after infusion. Alterations in the acini, comprising fusion of secretory granules, vacuole formation and dilation of the acinar lumina and intercellular canaliculi, were observed. At later times, atrophy of the parenchymal cells occurred together with an apparent proliferation of the connective-tissue stroma, as well as an increase in the number of small blood vessels. An inflammatory cell-infiltrate was seen in both groups of animals, but was most prominent in glands subjected to heavy parenchymal filling. The infiltrate, comprised primarily of macrophages and polymorphonuclear leukocytes, reached a peak at 20 h after infusion. At later times, mast cells and occasional eosinophils were seen. The observed alterations and the pattern of recovery are most likely due to the induced intraglandular pressure and the following inflammatory reaction. It is also possible that the changes, to some extent, are influenced by the presence of the contrast medium in the tissue.

Effects of selective alpha 1 and alpha 2 adrenoceptor active drugs on 86Rb+ efflux from pieces of rat parotid gland

Minute pieces of rat parotid gland were used in studies of adrenergic regulation of K+ efflux using 86Rb+ as a probe for K+. Noradrenaline induced a concentration-dependent RB+ efflux, whereas the beta 1-selective agonist prenalterol was without effect. On the other hand, the beta 2-selective drug, terbutaline, at high concentrations displayed a small enhancement of Rb+-secretion. The selective alpha 1-adrenoceptor drug, phenylephrine, was as potent as noradrenaline, whereas the alpha 2-agonist clonidine had only a small effect. The noradrenaline-induced Rb+-efflux was effectively inhibited in the presence of prazosin, an alpha 1-blocker, whereas the alpha 2-antagonist, yohimbine, was roughly 50 times less potent. The results suggest that catecholamine-induced K+-secretion from the rat parotid gland is mediated via activation of post-synaptic alpha-adrenoceptors of the alpha 1-subtype.

A kinetic study of rat salivary gland alkaline phosphatase and its inhibition by cadmium

Alkaline phosphatase, confined to myoepithelial cells and blood capillaries in rat submandibular salivary gland (SSG), may participate in the regulation of salivary flow. To determine whether the alkaline phosphatase of SSG has unique properties, comparative kinetic and inhibition studies on enzymes from SSG, intestine and kidney were performed. The Km values (at optimal pH for each tissue) of 0.34, 0.55 and 0.49 mM with p-nitrophenylphosphate for the enzymes from SSG, kidney and small intestine respectively were similar. However, in the presence of cadmium the Ki values of 0.08 and 0.12 microM for the enzymes from SSG and kidney respectively were different from the value of 1.86 microM for the enzyme from small intestine. Differences in Ki values suggest differences in biochemical properties between the enzyme from small intestine and that isolated from SSG or kidney.

A light and electron microscopic study of the distribution and effects of water-soluble radiographic contrast medium after retrograde infusion into the rat submandibular gland

For microscopic visualization, horseradish peroxidase (HRP; 10 mg/ml) was added to the contrast medium. Some glands were infused with saline solution containing HRP. During continuous infusion, the intraglandular pressure was recorded. Infusion was stopped at different phases of the pressure curve and the glands fixed by vascular perfusion. Morphological alterations, principally dilatation of the intralobular ducts, were most pronounced in the intercalated duct segment. HRP was first observed in the lumina of the intralobular ducts and acini but gained access to the intercellular spaces thought the apical junctional complexes and subsequently surrounded various cellular components. Eventually the tracer was found in blood and lymphatic vessels. Because of an uneven distribution of the tracer and variation in the degree of filling in different areas of the same gland, the development of the intraglandular pressure could not be directly correlated with specific morphological alterations but is thought to reflect all events occurring in the tissue at a particular time.

Carbon dioxide decreases the intracellular potassium activity in frog muscle [proceedings]

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