Regulation of parotid salivary proteins by glucocorticoids

Long-term dexamethasone treatment diminishes store-operated Ca2+ entry in salivary acinar cells

Corticosteroids are used in the treatment of many diseases; however, they also induce various side effects. Dexamethasone is one of the most potent corticosteroids, and it has been reported to induce the side effect of impaired salivary gland function. This study aimed to evaluate the effects of dexamethasone on mouse submandibular gland function to gain insight into the mechanism of dexamethasone-induced salivary hypofunction. The muscarinic agonist carbachol (CCh) induced salivary secretion and was not affected by short-term dexamethasone treatment but was decreased following long-term dexamethasone administration. The expression levels of the membrane proteins Na⁺-K⁺-2Cl^- cotransporter, transmembrane member 16A, and aquaporin 5 were comparable between the control and long-term dexamethasone treatment groups. The CCh-induced increase in calcium concentration was significantly lower in the presence of extracellular Ca²⁺ in the long-term dexamethasone treatment group compared to that in the control group. Furthermore, CCh-induced salivation in the absence of extracellular Ca²⁺ and Ca²⁺ ionophore A23187-induced salivation was comparable between the control and long-term dexamethasone treatment groups. Moreover, salivation induced by the Ca²⁺-ATPase inhibitor thapsigargin was diminished in the long-term dexamethasone treatment group. In summary, these results demonstrate that short-term dexamethasone treatment did not impair salivary gland function, whereas long-term dexamethasone treatment diminished store-operated Ca²⁺ entry, resulting in hyposalivation in mouse submandibular glands.

Long-term dexamethasone treatment alters the histomorphology of acinar cells in rat parotid and submandibular glands

Glucocorticoids (GCs) induce insulin resistance (IR), a condition known to alter oral homeostasis. This study investigated the effects of long-term dexamethasone administration on morphofunctional aspects of salivary glands. Male Wistar rats received daily injections of dexamethasone [0.1 mg/kg body weight (b.w.), intraperitoneally] for 10 days (DEX), whereas control rats received saline. Subsequently, glycaemia, insulinaemia, insulin secretion and salivary flow were analysed. The parotid and submandibular glands were collected for histomorphometric evaluation and Western blot experiments. The DEX rats were found to be normoglycaemic, hyperinsulinaemic, insulin resistant and glucose intolerant (P < 0.05). DEX rat islets secreted more insulin in response to glucose (P < 0.05). DEX rats had significant reductions in the masses of the parotid (29%) and submandibular (16%) glands (P < 0.05) that was associated with reduced salivary flux rate. The hypotrophy in both glands observed in the DEX group was associated with marked reduction in the volume of the acinar cells in these glands of 50% and 26% respectively (P < 0.05). The total number of acinar cells was increased in the submandibular glands of the DEX rats (P < 0.05) but not in the parotid glands. The levels of proteins related to insulin and survival signalling in both glands did not differ between the groups. In conclusion, the long-term administration of dexamethasone caused IR, which was associated with significant reductions in both mass and flux rate of the salivary glands. The parotid and submandibular glands exhibited reduced acinar cell volume; however, the submandibular glands displayed acinar hyperplasia, indicating a gland-specific response to GCs. Our data emphasize that GC-based therapies and insulin-resistant states have a negative impact on salivary gland homeostasis.

Cloning and Functional Study of Porcine Parotid Hormone, a Novel Proline-rich Protein

A parotid gland hormone that stimulates intradentinal fluid movement is believed to play a significant role in maintaining the vitality of dentin. This hormone has been purified from porcine parotid glands and partially sequenced in our previous study (Tieche, J. M., Leonora, J., and Steinman, R. R. (1980) Endocrinology 106, 1994-2005). We now report the cloning and functional study of porcine cDNAs that code for this hormone and its complete amino acid sequence. Three cDNA clones were isolated from a porcine parotid cDNA library. The last 30 amino acids encoded by two of the cDNAs agreed with the amino acid sequence of the isolated parotid hormone. In situ hybridization and immunohistochemical staining demonstrated that the acinar cells of the parotid glands were the primary location for both the parotid hormone-related mRNAs and the translation products. A 216-bp fragment of the cDNA that contains the coding sequence for the porcine hormone was subcloned into an expression vector, and the protein expression was detected by immunoblot analysis and quantified by enzyme-linked immunosorbent assay. In addition, the 30-amino acid parotid hormone was synthesized. Both the expressed and the synthetic proteins were biologically active in that they enhanced intradentinal fluid movement as measured by intradentinal dye penetration.

Neuroendocrine regulation of salivary IgA synthesis and secretion: implications for oral health

Secretory immunoglobulin A (S-IgA) represents the main adaptive immune mechanism in the oral cavity. The regulation of secretion and synthesis of S-IgA is not only dependent on prior antigenic stimulation, but is also under strong neuroendocrine control. Thus, alterations in neuroendocrine functioning (such as induced by stress, exercise, pregnancy, menstrual cycle, and pharmacological interventions) may affect salivary IgA levels. This review deals with the neuroendocrine regulation of synthesis and secretion of salivary IgA and its potential role in the maintenance of oral health.

Intralobular ducts of human major salivary glands contain leptin and its receptor

Leptin, a 16-kDa hormone, plays an important role in the control of food intake and in energy homeostasis both in rodents and in man. Leptin is mainly produced and secreted by adipocytes, but other tissues and gastric glands have also recently been shown to produce it in a dual (endocrine and exocrine) mode. In addition, a leptin receptor has been detected in taste cells of mouse circumvallate papillae and in rat intestinal epithelium. These data prompted us to carry out a detailed study of human salivary glands as potential leptin-producing organs. Biopsies of salivary glands (submandibular and parotid) obtained from male and female patients during surgery for different clinical indications were subjected to immunohistochemical study for the presence of leptin, its functional receptor, insulin and glucagon. The presence and cellular distribution of glucocorticoid receptor in leptin-secreting cells were also investigated. Double immunohistochemical staining (silver-gold intensification and avidin-biotin-peroxidase) was used for the visualization of glucocorticoid receptor and leptin labelling, respectively. The results show that intralobular duct cells of submandibular and parotid glands are immunoreactive for leptin, leptin receptor and glucagon but not for insulin. Leptin was also detected in some microglobules in whole saliva obtained from four healthy volunteers. Co-localization for leptin, leptin receptor and glucocorticoid receptor in the same cell type suggested a functional relationship between glucocorticoid hormone and leptin secretion also at the level of the salivary glands.

High-resolution electrophoretic analysis of rat parotid salivary proteins

Silver staining and high-resolution electrophoretic methods have been used to compare the protein composition of rat parotid saliva evoked in response to (i) parasympathetic stimulation (including the nonadrenergic, noncholinergic, atropine-associated secretion), (ii) sympathetic stimulation, or (iii) the infusion of neuropeptides with secretagogue activity (substance P, calcitonin gene-related peptide, neuropeptide Y, or vasoactive intestinal peptide). The different stimuli influenced the protein concentration and flow rate of the evoked secretion but had little effect upon the protein composition of the saliva. In contrast to earlier studies using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Coomassie blue staining, the combination of silver staining and two-dimensional electrophoresis (2-DE) revealed many newly detected proteins. The results indicate that the protein composition of rat parotid saliva is more complex than previously reported but is unaffected by the mode of stimulation.

The effect of adrenergic agonists and antagonists on the expression of proteins in rat submandibular and parotid glands

The present investigation was undertaken to study the effect of adrenoreceptor modulators on the expression of salivary proteins. Sprague-Dawley rats were treated for 10 consecutive days with adrenergic agonists isoproterenol, dobutamine, terbutaline, salbutamol, methoxyphenamine, or methoxamine. Antiserum to selected salivary proteins was used to compare the concentration of these proteins in the submandibular and parotid glands of treated animals. Chronic treatments of rats (50 mumol/kg body weight for 10 d) with either isoproterenol or dobutamine induced synthesis of a cysteine-proteinase inhibitor (cystatin) in the submandibular glands. When isoproterenol was injected concomitantly with the mixed beta-antagonist propranolol or the beta 1-adrenergic antagonists metaprolol, protocol, or atenolol, the induction of cystatin was totally suppressed. However, the beta 2-antagonist, ICI-118551, produced only partial reduction in cystatin induction elicited by isoproterenol. On the contrary, rats treated with either isoproterenol or beta 1-agonists demonstrated a significantly reduced concentration of serine-proteinase kallikrein in submandibular glands. The decrease observed in submandibular kallikrein of rats treated with isoproterenol was prevented by concomitant treatment with beta 1-antagonists but not with beta 2-antagonists. Because kallikreins are produced by ductal cells and cystatins are produced by acinar cells of submandibular glands, these observations suggest that there may be differential control of expression of proteins synthesized by ductal and acinar cells. Chronic treatment of rats with nonselective beta-agonist isoproterenol or beta 1-selective agonists increased markedly the proline-rich proteins (PRP) in parotid glands, but the parotid amylase concentration was not significantly affected by beta-adrenergic agonists.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of thyroxine in the regulation of rat parotid salivary protein composition

This study tested the role of thyroxine in the regulation of the protein composition of rat parotid saliva. Thyro-parathyroidectomy was performed on two groups of rats, one of which subsequently received thyroxine replacement; the third group was sham-operated. Parotid saliva was collected on the eighth day after surgery, with pilocarpine and isoproterenol used as a secretory stimulus. The volume of saliva collected in 30 min from the thyro-parathyroidectomized rats was 55% less than that collected from sham-operated rats. In the thyro-parathyroidectomized rats, the protein concentration as measured by absorption at 215 nm was unaltered, but that measured by the Lowry procedure was 43% higher. Spectrophotometric scans of Coomassie Blue-stained gels following sodium dodecylsulfate polyacrylamide gel electrophoresis of the secreted proteins showed an 18% reduction in the proportion of protein attributable to amylase and a 43% reduction in proportion of acidic and basic proline-rich proteins following thyro-parathyroidectomy; deoxyribonuclease and two other major secretory proteins (Fraction I and Fraction V) were increased (38%, 20%, and 46%, respectively). These changes in flow rate, protein concentration by the Lowry assay, and protein composition were prevented by treatment of thyro-parathyroidectomized rats with thyroxine replacement and are in opposition to those changes we reported earlier for hyperthyroid rats. The results indicate that the flow of saliva as well as the synthesis of the various salivary proteins are influenced by thyroxine.

Changes in rat parotid saliva protein composition following chronic reserpine treatment and their relation to inanition

Chronic administration of the catecholamine-depleting agent, reserpine (0.5 mg/kg), resulted in a reduction in food intake after 3 days. To differentiate effects of the drug from those of reduced food intake a pair-fed group, whose daily caloric intake was restricted to the amount consumed by the reserpine-treated rats, was included. After 7 days, both the reserpine-treated and pair-fed control exhibited a marked reduction in the volume of saliva collected in a 30 min interval following a secretory stimulus compared to untreated ad libitum-fed controls, and the proportion of salivary proteins attributable to acidic and basic proline-rich proteins and to minor 1b protein were decreased whereas deoxyribonuclease was increased. For two of the salivary proteins (fractions I and V) changes for the reserpine-treated and pair-fed groups were different. Fraction I was reduced in both groups, but exhibited a greater decrease in the pair-fed than in the reserpine-treated, whereas fraction V was significantly increased only in the pair-fed group. Thus many of the salivary changes associated with reserpine treatment may have resulted from the change in feeding habits and not from reserpine treatment per se. The study demonstrates the importance of controlling for food intake under experimental circumstances which may lead to a marked change in daily feeding habits.