The salivary proteome in relation to oral mucositis in autologous hematopoietic stem cell transplantation recipients: a labelled and label-free proteomics approach

BACKGROUND

Oral mucositis is a frequently seen complication in the first weeks after hematopoietic stem cell transplantation recipients which can severely affects patients quality of life. In this study, a labelled and label-free proteomics approach were used to identify differences between the salivary proteomes of autologous hematopoietic stem cell transplantation (ASCT) recipients developing ulcerative oral mucositis (ULC-OM; WHO score ≥ 2) or not (NON-OM).

METHODS

In the TMT-labelled analysis we pooled saliva samples from 5 ULC-OM patients at each of 5 timepoints: baseline, 1, 2, 3 weeks and 3 months after ASCT and compared these with pooled samples from 5 NON-OM patients. For the label-free analysis we analyzed saliva samples from 9 ULC-OM and 10 NON-OM patients at 6 different timepoints (including 12 months after ASCT) with Data-Independent Acquisition (DIA). As spectral library, all samples were grouped (ULC-OM vs NON-OM) and analyzed with Data Dependent Analysis (DDA). PCA plots and a volcano plot were generated in RStudio and differently regulated proteins were analyzed using GO analysis with g:Profiler.

RESULTS

A different clustering of ULC-OM pools was found at baseline, weeks 2 and 3 after ASCT with TMT-labelled analysis. Using label-free analysis, week 1-3 samples clustered distinctly from the other timepoints. Unique and up-regulated proteins in the NON-OM group (DDA analysis) were involved in immune system-related processes, while those proteins in the ULC-OM group were intracellular proteins indicating cell lysis.

CONCLUSIONS

The salivary proteome in ASCT recipients has a tissue protective or tissue-damage signature, that corresponded with the absence or presence of ulcerative oral mucositis, respectively.

TRIAL REGISTRATION

The study is registered in the national trial register (NTR5760; automatically added to the International Clinical Trial Registry Platform).

β-Adrenergic signaling induces Notch-mediated salivary gland progenitor cell control

β-Adrenergic signaling blockade is a mainstay of hypertension management. One percent of patients taking β-blockers develop reduced salivary gland (SG) function. Here we investigate the role of SG progenitor cells in β-blocker-induced hyposalivation, using human SG organoid cultures (SGOs). Compared with control SGs, initial low SG progenitor cell yield from patients taking β-blockers was observed. When passaged, these SGOs recovered self-renewal and upregulated Notch pathway expression. Notch signaling was downregulated in situ in β-adrenergic receptor-expressing luminal intercalated duct (ID) cells of patients taking β-blockers. Control SGOs treated with β-adrenergic agonist isoproterenol demonstrated increased proportion of luminal ID SGO cells with active Notch signaling. Control SGOs exposed to isoproterenol differentiated into more mature SGOs (mSGOs) expressing markers of acinar cells. We propose that β-blocker-induced Notch signaling reduction in luminal ID cells hampers their ability to proliferate and differentiate into acinar cells, inducing a persistent hyposalivation in some patients taking β-blocking medication.

•

SG organoids from patients taking β-adrenergic blockers show low yield

•

Notch signaling in parotid SG luminal ID cells decreases with β-blocker use

•

β-Adrenergic stimulation induces proliferation of parotid SG luminal ID cells

•

β-Adrenergic-induced Notch activity stimulates SGO differentiation into mSGOs

Disease-Induced Changes in Salivary Gland Function and the Composition of Saliva

Although the physiological control of salivary secretion has been well studied, the impact of disease on salivary gland function and how this changes the composition and function of saliva is less well understood and is considered in this review. Secretion of saliva is dependent upon nerve-mediated stimuli, which activate glandular fluid and protein secretory mechanisms. The volume of saliva secreted by salivary glands depends upon the frequency and intensity of nerve-mediated stimuli, which increase dramatically with food intake and are subject to facilitatory or inhibitory influences within the central nervous system. Longer-term changes in saliva secretion have been found to occur in response to dietary change and aging, and these physiological influences can alter the composition and function of saliva in the mouth. Salivary gland dysfunction is associated with different diseases, including Sjögren syndrome, sialadenitis, and iatrogenic disease, due to radiotherapy and medications and is usually reported as a loss of secretory volume, which can range in severity. Defining salivary gland dysfunction by measuring salivary flow rates can be difficult since these vary widely in the healthy population. However, saliva can be sampled noninvasively and repeatedly, which facilitates longitudinal studies of subjects, providing a clearer picture of altered function. The application of omics technologies has revealed changes in saliva composition in many systemic diseases, offering disease biomarkers, but these compositional changes may not be related to salivary gland dysfunction. In Sjögren syndrome, there appears to be a change in the rheology of saliva due to altered mucin glycosylation. Analysis of glandular saliva in diseases or therapeutic interventions causing salivary gland inflammation frequently shows increased electrolyte concentrations and increased presence of innate immune proteins, most notably lactoferrin. Altering nerve-mediated signaling of salivary gland secretion contributes to medication-induced dysfunction and may also contribute to altered saliva composition in neurodegenerative disease.

Significant salivary changes in relation to oral mucositis following autologous hematopoietic stem cell transplantation

The aim of this multicentre, longitudinal study was to determine salivary changes in relation to oral mucositis (OM) in multiple myeloma patients following high-dose melphalan and autologous hematopoietic stem cell transplantation (ASCT). Unstimulated and stimulated whole-mouth saliva samples (UWS and SWS) were collected before ASCT, 1×/wk during the hospitalisation phase, and 3 and 12 months post-ASCT. During the hospitalisation period OM was scored 3×/wk (WHO system). Flow rate, pH, total protein concentration (Nanodrop), albumin, lactoferrin, neutrophil defensin-1 (HNP1), total IgA and S100A8/A9 (ELISA) were determined. Mixed models were used to evaluate differences between ulcerative (u)OM (≥2 WHO, n = 20) and non-uOM (n = 31) groups. Until 18 days after ASCT, flow rate, pH, total IgA and HNP1 levels decreased in UWS and/or SWS, while log lactoferrin levels were significantly increased (UWS: p = 0.016 95% CI [0.36, 3.58], SWS: p < 0.001 95% CI [1.14, 3.29]). Twelve months post-ASCT, salivary protein levels were similar to baseline except for log total IgA, which was higher (UWS: p < 0.001 95% CI [0.49, 1.29], SWS: p < 0.001 95% CI [0.72, 1.45]). No differences between uOM and non-uOM groups were observed. Changes in salivary proteins indicated an inflammatory reaction in salivary glands coinciding with mucosal and systemic reactions in response to high-dose melphalan.

Salivary secretion in health and disease

Saliva is a complex fluid produced by 3 pairs of major salivary glands and by hundreds of minor salivary glands. It comprises a large variety of constituents and physicochemical properties, which are important for the maintenance of oral health. Saliva not only protects the teeth and the oropharyngeal mucosa, it also facilitates articulation of speech, and is imperative for mastication and swallowing. Furthermore, saliva plays an important role in maintaining a balanced microbiota. Thus, the multiple functions provided by saliva are essential for proper protection and functioning of the body as a whole and for the general health. A large number of diseases and medications can affect salivary secretion through different mechanisms, leading to salivary gland dysfunction and associated oral problems, including xerostomia, dental caries and fungal infections. The first part of this review article provides an updated insight into our understanding of salivary gland structure, the neural regulation of salivary gland secretion, the mechanisms underlying the formation of saliva, the various functions of saliva and factors that influence salivary secretion under normal physiological conditions. The second part focuses on how various diseases and medical treatment including commonly prescribed medications and cancer therapies can affect salivary gland structure and function. We also provide a brief insight into how to diagnose salivary gland dysfunction.

Salivary functions in mastication, taste and textural perception, swallowing and initial digestion

Saliva exerts multiple functions in relation to the initial digestive processes taking place in the upper parts of the gastrointestinal tract. Ingestion of food and beverages, in turn, is a strong stimulus for secretion of saliva with a differential composition depending on the neuronal stimulation pattern. This review paper provides insight into the mechanisms by which saliva acts in relation to taste, mastication, bolus formation, enzymatic digestion and swallowing. Also, the protective functions of saliva including maintenance of dental and mucosal integrity will be discussed as they indirectly influence the digestive process. The final part of this study focuses on the implications of xerostomia and salivary gland dysfunction on gastrointestinal functions.

Early salivary changes in multiple myeloma patients undergoing autologous HSCT

OBJECTIVE

One explorative observational study in two parts was performed to examine early salivary changes in relation to oral mucositis (OM) in multiple myeloma patients treated with high-dose melphalan and autologous haematopoietic stem cell transplantation (HSCT). As cryotherapy was introduced after part A as regular care, its effect on OM could be evaluated.

METHODS

Unstimulated whole-mouth saliva (UWS) and stimulated whole-mouth saliva (SWS) were collected, and OM was scored with the Oral Mucositis Nursing Instrument (OMNI) at days -3, 0, 4, 7, 11 and 14 after HSCT. Salivary flow rate, total protein (BCA), mucin 5B, albumin (western blot), total IgA, lactoferrin and myeloperoxidase levels (ELISA) were determined.

RESULTS

Trends of decreasing UWS and SWS flow rates and total IgA levels were observed. At days 7 and 11, increases in lactoferrin and albumin levels were found in UWS and SWS. A positive correlation was found between OMNI scores and albumin and lactoferrin levels in SWS (R²  = .56, p = .029 and R²  = .49, p = .043, respectively). In part B, cryotherapy significantly lowered peak OMNI scores.

CONCLUSION

Compositional changes in saliva reflecting inflammation were found in the first days after HSCT, and the use of cryotherapy in the second part was associated with decreased OM severity.

The effect of parotid gland-sparing intensity-modulated radiotherapy on salivary composition, flow rate and xerostomia measures

OBJECTIVES

To describe parotid gland (PG) saliva organic and inorganic composition and flow rate changes, after curative intensity-modulated radiotherapy (IMRT) for head and neck cancer (HNC), and analyse the relationship between PG saliva analytes and xerostomia measures.

METHODS AND MATERIALS

Twenty-six patients recruited to five prospective phase 2 or 3 trials which assessed toxicity and efficacy of IMRT by HNC subsite, provided longitudinal PG saliva. Salivary flow rate, and subjective and objective xerostomia measures were prospectively collected and saliva tested for inorganic and organic analytes. Statistical comparisons of longitudinal analyte changes and analysis for a relationship between dichotomized xerostomia score and saliva analytes were performed.

RESULTS

One hundred and forty-two PG saliva samples from 26 patients were analysed. At 3-6 months after IMRT, stimulated and unstimulated saliva showed significantly decreased flow rate, total protein (TP) secretion rate, phosphate concentration and increased lactoferrin (LF) concentration. Stimulated saliva alone had elevated LF secretion rate and beta-2-microglobulin (B₂ M) concentration with decreased calcium (Ca²⁺ ) and magnesium (Mg²⁺ ) concentrations and Ca²⁺ secretion rate. At >12 months, under stimulated and unstimulated conditions, increased LF concentration and decreased Mg²⁺ and phosphate concentration persisted and, in stimulated saliva, there was decreased potassium (K⁺ ) and Mg²⁺ concentration. Unstimulated TP secretion rate was lower in the presence of high-grade xerostomia. Otherwise, no relationship between xerostomia grade and PG salivary flow rate, TP and Ca²⁺ secretion rate was found.

CONCLUSION

Fewer significant differences in PG saliva analytes >12 months after IMRT indicate good functional recovery. Residual xerostomia after IMRT will only be further reduced by addressing the sparing of subsites of the PG or other salivary gland tissues, in addition to the PG.

Salivary Proteins Interact with Dietary Constituents to Modulate Tooth Staining

Dietary components rich in polyphenols—for example, tea and red wine—are thought to cause tooth staining. In the present study, hydroxyapatite was used as a model of enamel for study of the influence of salivary proteins on the binding of different polyphenols to hydroxyapatite in vitro. Neither salivary protein pellicles nor salivary proteins in solution significantly altered the binding of the small polyphenol epigallocatechin to hydroxyapatite. However, hydroxyapatite binding of anthocyanin, a small grape-skin-derived polyphenol, or the larger polyphenols of black tea was increased by the presence of salivary proteins, either as a pellicle or in solution. Proline-rich proteins were enriched from parotid saliva and found to increase binding of anthocyanin and black tea polyphenols to hydroxyapatite, while enriched histatins did not increase binding. It is concluded that some salivary proteins, including proline-rich protein, can mediate increased staining of enamel by red-wine- and black-tea-derived polyphenols.

Salivary Gland Dysplasia in Fgf10 Heterozygous Mice: A New Mouse Model of Xerostomia

Xerostomia, or chronic dry mouth, is a common syndrome caused by a lack of saliva that can lead to severe eating difficulties, dental caries and oral candida infections. The prevalence of xerostomia increases with age and affects approximately 30% of people aged 65 or older. Given the large numbers of sufferers, and the potential increase in incidence given our aging population, it is important to understand the complex mechanisms that drive hyposalivation and the consequences for the dentition and oral mucosa. From this study we propose the Fgf10 +/- mouse as a model to investigate xerostomia. By following embryonic salivary gland development, in vivo and in vitro, we show that a reduction in Fgf10 causes a delay in branching of salivary glands. This leads to hypoplasia of the glands, a phenotype that is not rescued postnatally or by adulthood in both male and female Fgf10 +/- mice. Histological analysis of the glands showed no obvious defect in cellular differentiation or acini/ductal arrangements, however there was a significant reduction in their size and weight. Analysis of saliva secretion showed that hypoplasia of the glands led to a significant reduction in saliva production in Fgf10 +/- adults, giving rise to a reduced saliva pellicle in the oral cavity of these mice. Mature mice were shown to drink more and in many cases had severe tooth wear. The Fgf10 +/- mouse is therefore a useful model to explore the causes and effects of xerostomia.

Clinical assessment of oral dryness: development of a scoring system related to salivary flow and mucosal wetness

OBJECTIVE

The aim of this study was to develop a clinical oral dryness score (CODS) for routine use in assessment of xerostomia patients and determine its relationship with salivary flow rates and mucosal wetness.

STUDY DESIGN

CODS was determined from 10 features of oral dryness, each scoring as 1 point for a total score of 0-10. CODS, salivary flow rates, and mucosal wetness were measured in 100 patients and 50 healthy control subjects. The reproducibility of CODS was 0.89-0.96 (intraclass correlation coefficient).

RESULTS

The mean ± SD CODS in patients was 6.0 ± 1.6 compared with 1.0 ± 0.9 for control subjects (P < .001), and the highest mean value was in the primary Sjögren syndrome group. There was a general inverse relationship in patients between mean CODS and salivary flow rate (P < .01) and mean CODS and mucosal wetness (P < .01).

CONCLUSIONS

The CODS was found to be useful, easy to use, and reliable for routine assessment of the severity of dry mouth.

Activation of mTOR coincides with autophagy during ligation-induced atrophy in the rat submandibular gland

Salivary gland atrophy is a common consequence of pathology, including Sjögren's syndrome, irradiation therapy and obstructive sialadenitis. During severe atrophy of the rat submandibular gland caused by excretory duct ligation, the majority of acinar cells disappear through apoptosis, whereas ductal cells proliferate and dedifferentiate; yet, the gland can survive in the atrophic state almost indefinitely, with an ability to fully recover if deligated. The control mechanisms governing these observations are not well understood. We report that ~10% of acinar cells survive in ligation-induced atrophy. Microarray and quantitative real-time PCR analysis of ligated glands indicated sustained transcription of acinar cell-specific genes, whereas ductal-specific genes were reduced to background levels. After 3 days of ligation, activation of the mammalian target of rapamycin (mTOR) pathway and autophagy occurred as shown by phosphorylation of 4E-BP1 and expression of autophagy-related proteins. These results suggest that activation of mTOR and the autophagosomal pathway are important mechanisms that may help to preserve acinar cells during atrophy of salivary glands after injury.

Investigating the relationship between hyposalivation and mucosal wetness

BACKGROUND

Mucosal wetness (MW) reflects the layer of residual saliva that covers the oral mucosal surfaces.

OBJECTIVES

The aim of this study was to determine MW at different oral mucosa sites and to investigate the relationship between MW, unstimulated whole salivary flow rates (UWS) and Clinical Oral Dryness Score (CODS).

METHOD

A total of 100 dry mouth patients and 50 healthy subjects participated in the study. MW was sampled with filter paper strips at four sites inside the mouth; anterior hard palate (AHP), buccal mucosa (BUC), anterior tongue (AT), lower lip (LL) and measured with a micro-moisture meter. Reproducibility was assessed by repeated sampling and diurnal variation was examined.

RESULTS

Mucosal wetness in healthy subjects differed according to site and means±SD were; AHP (11± 11.7μm), BUC (32±14.8μm), AT (65±17.2μm), and LL (25 ±13.5μm). Dry mouth patients with reduced UWS showed increased CODS. MW at all four sites was significantly reduced (P<0.05) in dry mouth patients compared with the healthy subjects. Reproducibility of MW measurement using the intra-class correlation coefficient showed agreement at different visits within subject. MW of the AT showed a positive correlation with UWS (P<0.05).

CONCLUSION

Mucosal wetness is a reliable measure of oral dryness and had a positive correlation with UWS.

Altered plasticity of the parasympathetic innervation in the recovering rat submandibular gland following extensive atrophy

Adult rat submandibular glands have a rich autonomic innervation, with parasympathetic and sympathetic nerves working in synergy rather than antagonistically. Ligation of the secretory duct rapidly causes atrophy and the loss of most acini, which are the main target cell for parasympathetic nerves. Following deligation, there is a recovery of gland structure and function, as assessed by autonomimetic stimulation. This study examines whether the parasympathetic nerves reattach to new target cells to form functional neuro-effector junctions. Under recovery anaesthesia, the submandibular duct of adult male rats was ligated via an intra-oral approach to avoid damaging the chorda-lingual nerve. Four weeks later, rats were either killed or anaesthetized and the ligation clip removed. Following a further 8 weeks, both submandibular ducts were cannulated under terminal anaesthesia. Salivary flows were then stimulated electrically (chorda-lingual nerve at 2, 5 and 10 Hz) and subsequently by methacholine (whole-body infusion at two doses). Glands were excised, weighed and divided for further in vitro studies or fixed for histological examination. Ligation of ducts caused 75% loss of gland weight, with the loss of most acinar cells. Of the remaining acini, only 50% were innervated despite unchanged choline acetyltransferase activity, suggesting few parasympathetic nerves had died. Following deligation, submandibular glands recovered half their weight and had normal morphology. Salivary flows from both glands (per unit of gland tissue) were similar when evoked by methacholine but greater from the deligated glands when evoked by nerve stimulation. This suggests that parasympathetic nerves had reattached to new target cells in the recovered glands at a greater ratio than normal, confirming reinnervation of the regenerating gland.

Acute salivary gland hypofunction in the duct ligation model in the absence of inflammation

Objective

The commonly associated aetiology of salivary gland inflammation and salivary hypofunction has led to the widely held belief that inflammation causes salivary gland hypofunction. Indeed, our own recent study seemed to support this contention. Here, we tested the hypothesis that, in an acute duct ligation model, eliminating inflammation the submandibular gland would recover normal function.

Materials and methods

Ligation of the rat submandibular gland excretory duct for 24 h was used to induce inflammation and salivary gland hypofunction. A group of duct ligated rats was compared with a second group given dexamethasone, on the day of duct ligation. Twenty-four hours later salivary gland function was assessed and salivary glands were collected.

Results

Histology and myeloperoxidase activity assay revealed a profound decrease in inflammatory cell infiltration of ligated glands from rats given dexamethasone, compared with ligated glands in the absence of dexamethasone. Salivary flow rate evoked by methacholine was decreased (P < 0.01) by approximately 56% (ligated vs control, 79 ± 9 μl min⁻¹ g⁻¹vs 177 ± 11 μl min⁻¹ g⁻¹) and salivary flow from ligated dexamethasone-treated and ligated glands was similar.

Conclusion

Despite eliminating the inflammatory reaction in the ligated gland, salivary hypofunction was not reversed, suggesting that other mechanisms must be at work in the ligation-induced salivary hypofunction.

Rat salivary gland ligation causes reversible secretory hypofunction

AIM

To determine the influence of inflammation on salivary secretion. Secretion by salivary glands involves interactions between nerves, blood vessels and salivary cells. The present study investigated the effects of inflammation on rat submandibular gland function following acute ductal obstruction.

METHODS

Under recovery anaesthesia a metal clip was placed on the main duct of the submandibular gland. After 24 h salivary secretion was evoked by nerve and methacholine stimulation. For recovery experiments the clip was removed after 24 h and the animal left to recover for 3 days when salivary function was again assessed.

RESULTS

By 24 h of obstruction an inflammatory infiltrate had developed within the obstructed gland and stimulated salivary flows were just 20% of the normal secretion, whilst protein secretion and ion reabsorption were also severely impaired. If ductal obstruction was removed after 24 h the salivary function returned to normal after 3 days of recovery. In vitro analysis of cells from 24-h ligated glands revealed normal changes in intracellular calcium (the main secondary messenger involved in fluid secretion) in response to methacholine stimulation. Protein secretion from isolated cells indicated some changes in particular to methacholine-induced protein secretion although a significant protein secretion was still seen in response to isoprenaline - the main stimulus for protein secretion.

CONCLUSION

This report demonstrates reversible salivary inhibition associated with an inflammatory infiltrate within the salivary gland.

Effects of autonomic agonists and immunomodulatory cytokines on polymeric immunoglobulin receptor expression by cultured rat and human salivary and colonic cell lines

OBJECTIVE

Immunoglobulin A (IgA) is transported across glandular epithelial cells by polymeric immunoglobulin receptor (plgR), with each receptor molecule participating in only one round of transcytosis. Nerve-related stimuli rapidly increase salivary secretion of IgA, while concentrations are increased in the autoimmune disease Sjögren's syndrome. Our aim here was to determine whether autonomic agonists and cytokines present in Sjögren's-affected glands can up-regulate salivary cell plgR expression.

METHODS

Cultures of rat parotid acinar cells (PAR C5) and human submandibular gland ductal cells (HSG) were exposed to carbachol or adrenaline for 24 h and to interleukin-4 and/or interferon-gamma for 48 h. The human colonic cell line HT-29 served as a positive control for cytokine response. plgR mRNA was quantified by reverse transcription and real-time PCR and protein expression was examined by immunoblotting.

RESULTS

Carbachol increased plgR mRNA levels significantly in all cells but adrenaline did so only with PAR cells (P<0.05). HSG and HT-29 cells both up-regulated plgR gene transcription on exposure to interleukin-4 and interferon-gamma either alone or in combination (P<0.05). By contrast, production of plgR mRNA in PAR cells tended to decrease in response to all cytokine treatments. plgR protein levels rose in line with mRNA expression in cytokine-treated HT-29 cultures (P<0.05).

CONCLUSIONS

Autonomimetics can up-regulate plgR transcription in transformed and neoplastic salivary and colonic cells, although intracellular coupling mechanisms require further investigation. Immunomodulatory cytokines increased plgR expression in one of the salivary cell lines, but additional work is needed to establish whether this occurs in Sjögren's patients.

An in vitro model of chlorhexidine-induced tooth staining

BACKGROUND

Tooth staining is a common feature of chlorhexidine treatment for periodontal disease and there is a large variation between patients as to the degree of their tooth staining. Although the mechanism of tooth staining is uncertain, diet, smoking and oral hygiene appear probable factors.

OBJECTIVES

This study investigated the role of saliva in chlorhexidine-induced tooth staining and used tea as the staining agent in an in vitro model with hydroxyapatite mimicking teeth.

METHODS

Saliva has been used to create an acquired pellicle and in solution to mimic its effects in vivo. Using different combinations of tea, chlorhexidine and parotid saliva, substances binding to hydroxyapatite were analysed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Using this system, tea, chlorhexidine and salivary proteins were clearly identifiable following staining by Coomassie Brilliant Blue.

RESULTS

The results indicated that tea interacted with many salivary proteins, in particular proline-rich proteins and histatins. Chlorhexidine did not appear to complex with or precipitate salivary proteins nor prevent the formation of an acquired pellicle on the hydroxyapatite. In isolation, tea and chlorhexidine bound in small amounts to hydroxyapatite, but when added in combination, binding of both to hydroxyapatite was greatly increased. The acquired pellicle reduced chlorhexidine and tea binding, but conversely increased the binding of either tea or chlorhexidine alone to hydroxyapatite.

CONCLUSION

In conclusion, salivary proteins play an important role in the staining process and the combination of tea and chlorhexidine appears to be a very potent staining factor.

Preganglionic parasympathectomy decreases salivary SIgA secretion rates from the rat submandibular gland

Immunoglobulin A (IgA) is transported into saliva by salivary cells expressing the polymeric immunoglobulin receptor (pIgR). In rat salivary glands, autonomic nerves stimulate this process. To examine how nerves affect pIgR-mediated IgA secretion, the chorda-lingual nerve was sectioned. One week after preganglionic parasympathectomy, both the stimulated and unstimulated rates of salivary IgA secretion were reduced, despite similar glandular amounts of IgA. Biochemical analysis of cells from parasympathectomised and control glands indicated reduced membrane expression of pIgR. It appears the removal of long-term parasympathetic input has affected the routing of pIgR within salivary cells and reduced the SIgA transport into saliva.

Salivary secretion of immunoglobulin A by submandibular glands in response to autonomimetic infusions in anaesthetised rats

Salivary secretion of immunoglobulin A (lgA) by submandibular glands is increased by stimuli from autonomic nerves. Since it is unclear which specific autonomic receptors transduce such stimuli, we have infused autonomimetics intravenously and compared secretion of fluid, IgA and stored proteins (peroxidase and total protein) with secretory responses during electrical stimulation of the parasympathetic nerve supply in anaesthetized rats. The greatest secretion of IgA was evoked by the alpha-adrenoceptor agonist phenylephrine and this was reduced by the beta-adrenoceptor blocking drug propranolol. The secretion of fluid or proteins but not IgA was increased with frequency of nerve stimulation and dose of methacholine (cholinergic), isoprenaline (beta-adrenergic) or phenylephrine (alpha-adrenergic).

Constitutive secretion of immunoglobulin A and other proteins into lumina of unstimulated submandibular glands in anaesthetised rats

Salivary fluid secretion is dependent upon reflex stimuli mediated by autonomic nerves. In order to determine if immunoglobulin A (IgA) and salivary proteins are secreted in the absence of nerve stimulation, small volumes (< 2 microl) of saliva were consecutively collected from the submandibular duct of anaesthetised rats following rest pauses in order to sample the protein contents of the ductal system. Within the first 5 microl of such saliva collected by parasympathetic nerve stimulation, IgA and other salivary proteins reached peak concentrations that were over 20-fold greater than levels in parasympathetically stimulated saliva subsequently collected during a 5 min period of stimulation. Confocal microscopy of TRITC-labelled IgA added to live, acutely isolated submandibular acini indicated that it did not enter the lumina by paracellular leakage. IgG is thought to enter saliva by paracellular leakage but did not accumulate in luminal saliva in the present study. Electrophoresis suggested that the major proteins secreted in the absence of stimulation were the same as those present in subsequently stimulated saliva. It can be concluded that IgA and other major submandibular proteins are secreted into glandular lumina in the absence of nerve stimulation. The functional significance of such unstimulated protein secretion is at present unclear.

Ultrastructural histochemical studies of secretory granule replenishment in rat submandibular granular tubules after cyclocytidine-induced secretion

Rat submandibular glands have been examined electron microscopically at various times after degranulating the granular tubules by injecting cyclocytidine (75 mg/kg i.p.), to study events in the reformation of secretory granules in these cells. The changes were progressive but not synchronous in the cells. The first evidence of recovery was the re-appearance of glycogen particles 6 h after injection. Residual secretory granules were small and located periluminally at that time. More granules were present at 15 h after injection but they were still small and placed periluminally. There was more glycogen in the cells and some was present in aggregates. At 1 day after injection there were more secretory granules and they tended to be larger than previously. The secretory granules increased in size and number progressively thereafter and the cells appeared like normal controls by day 7. During the recovery, fusion profiles were seen between granules from 2 days onwards. Throughout, few Golgi complexes were detected and this may be related with the low glycosylation of the secretory proteins in these cells. The results confirm that the reformation of the secretory granules in granular tubule cells is a slow process that involves fusions of smaller granules.

Levels of pre-kallikrein in resting and stimulated human parotid and submandibular saliva

Salivary tissue kallikrein is stored in an active form in human salivary glands. Pre-kallikrein has been demonstrated in mixed saliva, but it is not clear if the various salivary glands contribute equally. This study set out to determine if pre-kallikrein is present in human parotid and submandibular salivas at rest, whether levels change during stimulation, and to compare the pattern of pre-kallikrein and kallikrein secretion with that of total protein. Resting and citric acid-stimulated parotid and submandibular, and gum-stimulated parotid saliva samples were collected from 6 healthy subjects. Salivary flows were determined gravimetrically. Total protein concentration and kallikrein enzymic activity were assayed using standard techniques. Pre-kallikrein was assayed following trypsinisation of duplicate samples. Pre-kallikrein was present in parotid and submandibular ductal saliva. Proportions of pre-kallikrein and active kallikrein were similar in salivas secreted at rest and during stimulation, and both outputs mirrored protein output in both major glands. Gum-stimulated parotid saliva showed lower activity than resting, and no differences were seen between resting and stimulated submandibular samples.

Chewing stimulates secretion of human salivary secretory immunoglobulin A

Immunoglobulin A (IgA) is the most abundant immunoglobulin in saliva and other mucosal secretions and plays an important role in mucosal immunity. The present study examined whether secretion of IgA, like other salivary proteins, is increased by reflex stimulation. Parotid saliva was collected from subjects into separate vials under resting conditions and during chewing-stimulated secretion over 45 min. Enzyme-linked immunosorbent assay (ELISA) indicated that chewing increased IgA secretion. The extent and pattern of the increase were similar to those of total protein and acinar cell amylase. SDS gel electrophoresis and Western blotting showed that high-molecular-weight forms of IgA-containing secretory component predominated in all saliva samples. Secretory component, the cleaved epithelial receptor for polymeric IgA, was secreted in a pattern very similar to that of IgA. It is concluded that chewing stimulates epithelial cell transcytosis of IgA and increases secretion of secretory IgA into saliva.

Sialochemical markers of salivary gland involvement with Sjögren's syndrome secondary to rheumatoid arthritis and primary biliary cirrhosis

Sjögren's syndrome is an autoimmune condition affecting the lacrimal and salivary glands and can be associated with rheumatoid arthritis and primary biliary cirrhosis. Parotid salivas collected from patients and normal controls were analysed for lactoferrin, IgA and beta2-microglobulin (measured by ELISA), and cystatin (measured by a enzyme inhibition assay). Output data provided less variable means, whilst expressing results as a proportion of the total protein provided greater specificity as markers for Sjögren's syndrome. Levels of specificity for IgA, lactoferrin and beta2-microglobulin were all high (100, 95 and 100%, respectively). Sensitivity levels of these markers (but not cystatin) tended to be similar for Sjögren's syndrome secondary to primary biliary cirrhosis (IgA, 25%; lactoferrin, 63%; and beta2-microglobulin, 50%), compared to Sjögren's syndrome secondary to connective tissue diseases such as rheumatoid arthritis (IgA, 50%; lactoferrin, 86%; and beta2-microglobulin; 38%).

Sympathetic decentralization abolishes increased secretion of immunoglobulin A evoked by parasympathetic stimulation of rat submandibular glands

Salivary secretion of immunoglobulin A (IgA) in response to electrical stimulation of the parasympathetic nerve supply was assessed bilaterally in the submandibular glands of anaesthetized rats 1 week following unilateral pre-ganglionic sympathectomy (decentralization). Nerve-mediated stimulation on the non-denervated side increased IgA secretion several fold above an unstimulated rate of secretion whereas sympathetic decentralization reduced the parasympathetically stimulated secretion of IgA without affecting the basal rate. Glandular levels of IgA were increased following decentralization compared to the control glands. Salivary levels of free secretory component (FSC), the cleaved polymeric immunoglobulin receptor (plgR), were increased by parasympathetic stimulation and reduced by sympathectomy, though not as much as IgA. The decreased secretion of FSC suggests a reduced production of plgR and may account in part, for reduced IgA secretion following long-term removal of sympathetic nerve impulses.

Nerve-evoked secretion of immunoglobulin A in relation to other proteins by parotid glands in anaesthetized rat

Secretion of fluid and proteins by salivary cells is under the control of parasympathetic and sympathetic autonomic nerves. In a recent study we have shown that, in the rat submandibular gland, autonomic nerves can also increase the secretion of IgA, a product of plasma cells secreted into saliva as SIgA (IgA bound to Secretory Component, the cleaved poly-immunoglobulin receptor). The present study aimed to determine if parotid secretion of SIgA is increased by autonomic nerves and to compare SIgA secretion with other parotid proteins stored and secreted by acinar and ductal cells. Assay of IgA in saliva evoked by parasympathetic nerve stimulation immediately following an extended rest period under anaesthesia indicated that it had been secreted into intraductal saliva in the absence of stimulation during the rest period. The mean rate of unstimulated IgA secretion (2.77+/-0.28 microg min(-1) g(-1)) and the 2.5-fold increase in IgA secretion evoked by parasympathetic stimulation were similar to results found previously in the rat submandibular gland. Sympathetic nerve stimulation increased SIgA secretion 2.7-fold, much less than in the submandibular gland. SDS-PAGE and Western blot analysis with anti-IgA and anti-Secretory Component antibodies confirmed that SIgA was the predominant form of IgA in saliva. Acinar-derived amylase and ductal-derived tissue kallikrein were more profoundly increased by parasympathetic and particularly sympathetic stimulation than SIgA. Overall, the results of the present study indicate that SIgA forms a prominent component of unstimulated parotid salivary protein secretion and that its secretion is similarly increased by stimulation of either autonomic nerve supply. The secretion of other parotid salivary proteins that are synthesized and stored by acinar or ductal cells is upregulated to a much greater extent by parasympathetic and particularly sympathetic stimulation.

Reflex secretion of proteins into submandibular saliva in conscious rats, before and after preganglionic sympathectomy

1. An indwelling catheter was placed in the left submandibular duct of rats, under pentobarbitone anaesthesia, and connected to an outflow cannula that emerged above the skull. 2. Saliva was collected from the outflow cannula in conscious rats, the same day after recovery from anaesthesia, under four different reflex conditions: grooming, heat exposure, rejection of a bitter tasting substance and feeding on softened chow, repeated in different orders. 3. Saliva flow was greatest for grooming and least for rejection. Protein concentrations were least with heat but much greater and similar for the other stimulations. Acinar peroxidase activity was high for feeding, intermediate for grooming and rejection, and again lowest with heat. Tubular tissue kallikrein activities were moderately low, being greatest with feeding and least with grooming. Secretory immunoglobulin A (SIgA) concentration was least with heat and similar for the other stimulations. 4. The next day, under pentobarbitone anaesthesia, the left preganglionic sympathetic trunk was sectioned (sympathetic decentralization) and, after recovery, the preceding stimulations were repeated. Flow of saliva showed little change, but protein and peroxidase concentrations and outputs decreased dramatically with grooming, rejection and feeding to levels similar to those with heat, which showed little change. Tissue kallikrein was lowered less dramatically, but the reductions in output were significant except with heat. Patterns of proteins resolved by electrophoresis changed for grooming, rejection and feeding and became similar to saliva from heat, which showed little change. No significant effects on SIgA concentrations occurred. 5. Gland weights from the sympathetically decentralized side were greater than from the intact side at the end of the experiments and histologically showed retention of acinar mucin. 6. Thus reflex sympathetic drive varied with the different stimulations; it was least during heat, but it had pronounced effects on acinar secretion of proteins during the other stimulations. At the same time this sympathetic drive had less impact on tissue kallikrein secretion from tubules and had little influence on flow or the concentration of SIgA secreted.

Precipitation of specific proteins by freeze-thawing of human saliva

Frozen saliva samples demonstrate a variable amount of precipitate on thawing depending on the type of secretion [submandibular-sublingual (SML) greater than parotid]. This precipitate has been resuspended using EDTA or removed by centrifugation by some workers and others do not mention it. Yet others collect the salivas into EDTA or centrifuge them before freezing. To determine the adsorption of proteins to hydroxyapatite, prior treatment with EDTA would be disadvantageous. The aim here was to determine if the protein pattern in parotid and SML saliva as demonstrated by sodium dodecyl sulphate gel electrophoresis is affected by the formation of precipitates. Portions of parotid and SML saliva were thawed and treated in the following ways: (a) mixed vigorously with a vortex mixer; (b) centrifuged to remove the precipitate; (c) mixed with EDTA (1 and 5 mmol final concentration for parotid and SML samples, respectively) to resuspend the precipitate. The samples were loaded on to gradient (5-20%) SDS gels and, following electrophoresis, the gels were stained with Coomassie brilliant blue R-250. The protein patterns obtained for (a) and (c) were the same. The centrifuged samples demonstrated loss of a specific band of less than 14 kDa, although this was less obvious in the parotid samples. The SML samples also showed a reduction in other lower molecular-weight proteins. This study demonstrates that precipitates in thawed frozen salivas contain specific proteins and that these samples require careful handling to avoid any alteration in the overall protein composition.

Immunoglobulin A secretion into saliva during dual sympathetic and parasympathetic nerve stimulation of rat submandibular glands

Salivary secretion of proteins from rat submandibular glands was studied using graded stimulation of the parasympathetic nerve in isolation, and then at a fixed rate in combination with graded sympathetic nerve stimulation. Increasing the frequency of parasympathetic nerve stimulation per se caused a gradual increase in the secretion of peroxidase (from acini) but only small increases in proteinase (from ductal cells) and IgA outputs. Dual stimulations, with an increasing frequency of sympathetic nerve stimulation on a background of low frequency parasympathetic nerve stimulation, showed that maximal acinar secretion of peroxidase required only a low frequency of additional sympathetic stimulation, whereas ductal secretion of kallikrein was greatest with the highest frequency of additional sympathetic stimulation (20 Hz in bursts). IgA secretion also required high frequency additional sympathetic stimulation in bursts for greatest output. Although a synergism occurred with parasympathetic plus sympathetic nerve stimulation for the secretion of both peroxidase and kallikrein it was not evident for the secretion of IgA. This presumably reflects a difference for exocytosis of proteins stored in granules (e.g. peroxidase and kallikrein) compared to those proteins continuously transported across the plasma membrane in vesicles by transcytosis. This work confirms that vesicular movement of secretory IgA can be increased by both parasympathetic and sympathetic nerve stimulation, but the frequency parameters differ for each nerve.

Double electrophoretic separation and lectin analyses of the component chains of secretory immunoglobulin A from human saliva

A new method is presented for the separation of secretory immunoglobulin A (SIgA) from salivary samples. Salivary proteins (from parotid or stimulated whole mouth saliva) were precipitated with methanol to concentrate SIgA from salivary samples whilst removing other salivary proteins. SIgA purified from breast milk and salivary proteins was separated by 10% sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) under nonreducing conditions. Following completion of electrophoresis the top strip of gel was removed and the proteins present reduced with dithiothreitol. The gel strip was then applied to the top of a second 10% SDS gel, and the proteins were electrophoresed and then stained by Coomassie Brilliant Blue R-250. Three major protein bands were stained in all samples corresponding in molecular mass to secretory component, alpha-heavy chain and light chains of SIgA. Separated proteins were also electroblotted onto nitrocellulose and stained by fluorescein isothiocyanate (FITC). Lectin analysis was then used to detect the O-glycans present on IgA1. Lectins from Helix aspersa and Arachis hypogaea were used to determine the amount of terminal N-acetyl galactosamine and nonsialylated O-glycans, respectively. Maclura pomifera lectin was used to determine the total amount of IgA1 present on the blots. The results indicate that SlgA in stimulated whole mouth saliva, stimulated parotid saliva and purified from breast milk contain similar O-glycans.

Ultrastructural histochemical studies of secretory processes in rat submandibular granular tubules during intermittent sympathetic nerve stimulation

Secretory changes in the cells of granular tubules in rat submandibular glands have been studied sequentially during electrical stimulation of their sympathetic nerves. Results were assessed in a series of biopsied lobes from the same gland, taken at different times during the sympathetic stimulation. Changes were not synchronous between adjacent cells and it appeared that the time for the onset of secretory events differed between cells but, once set in action, a chain of similar events occurred. Nevertheless, some cells appeared to remain refractory throughout. Initially, some alignment of granules to the adjacent plasma membrane occurred and occasional evidence for classical exocytosis was seen. However, from early on microvesicles appeared in more luminally located granule membranes and were associated with granule fusions, that became common and led to the formation of large irregular aggregates. Most of the secretion of granule contents appeared to be through openings of aggregates into lumina. With granule fusions the intra-membrane microvesicles became internalised and tended to increase in size with time; they were commonly expelled with the contents of the aggregates. Fragments of cytoplasm also became incorporated in aggregate formation. Cytoplasm, often containing glycogen, also formed luminal blebs over some granular tubule cells and appeared to pass into the secretion by an apocrine process. At the end of stimulation multivesicular bodies were seen in association with redundant aggregates.

O-linked glycosylation occurs on basic parotid salivary proline-rich proteins

Interactions between salivary glycoproteins and many oral bacteria have been shown to depend on O-linked glycans on salivary glycoproteins. Basic proline-rich proteins form the largest group of proteins within human parotid saliva. In the present study human parotid salivary glycoproteins were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis or two-dimensional electrophoresis, electroblotted onto nitrocellulose and probed with two biotin-labelled lectins from Maclura pomifera (MPA) and Arachis hypogaea (PNA) which are specific for O-linked (galactose beta 1,3 N-Acetylgalactosamine) glycans. Lectin binding was detected with avidin-biotin complex and enhanced chemiluminescence. Two-dimensional electrophoresis in combination with lectin binding indicated that only basic parotid salivary glycoproteins bind the lectin MPA. Following removal of terminal sialic acid residues by sialidase digestion the same glycoproteins were detected by the lectin PNA. Glycosidase digestion with endo-alpha-N-acetylgalactosaminidase (O-glycanase) in conjunction with sialidase eliminated MPA binding. Taken together these results indicate that many basic parotid salivary glycoproteins contain O-glycans, all of which are sialylated.

Lectin binding studies of parotid salivary glycoproteins in Sjögren's syndrome

Human parotid salivas were collected from patients with secondary Sjögren's syndrome and controls without disease or with drug-induced xerostomia. Parotid glycoproteins were separated by gradient sodium dodecyl sulphate gel electrophoresis (SDS-PAGE), electroblotted onto nitrocellulose membrane and probed with biotinylated lectins of characterised sugar specificities. The binding patterns of lectins from Maclura pomifera (MPA) and Arachis hypogaea (PNA) indicated that many parotid glycoproteins have sialylated O-linked glycans and that sialylation is not affected by disease. Binding by lectins from Ricinus communis (RCA-1), Limax flavus (LFA), Lotus tetragonolobus (LTA) and Ulex europaeus (UEA-1) appeared unaltered in secondary Sjögren's syndrome, suggesting no obvious change in N-glycosylation of parotid glycoproteins. Variations in binding patterns of most lectins was attributable to subject-to-subject variations in recognised polymorphic proteins. Dolichos biflorus agglutinin (DBA) consistently showed increased binding to a 75 kDa (Mr) protein in salivas from patients with secondary Sjögren's syndrome. The binding protein was identified as lactoferrin but found not to contain N-acetylgalactosamine, the sugar to which DBA binds. Binding of DBA to lactoferrin was dependent upon its saturation with iron, modified SDS-PAGE under nonreducing conditions resolved iron-free and iron-saturated lactoferrins and demonstrated increased levels of the iron-saturated form in secondary Sjögren's syndrome. Lectin binding studies of purified lactoferrins from saliva, milk, and polymorphonuclear neutrophils suggested that raised levels of lactoferrin in saliva originate from salivary cells and not from inflammatory cells. These results suggest that DBA binding provides greater specificity as an indicator of salivary gland disease than measurement of lactoferrin levels alone.

Enzyme histochemistry of tryptase in stomach mucosal mast cells of the mouse

We investigated the histochemical characteristics of mast cell tryptase in different mouse tissues. By use of peptide substrates, tryptase activity could be demonstrated in unfixed connective tissue mast cells in different tissues, including the stomach. Tryptase activity was better localized after aldehyde fixation and frozen sectioning, and under such conditions was also demonstrated in mucosal mast cells of the stomach but not in those of the gut mucosa. Double staining by enzyme histochemistry followed by toluidine blue indicated that the tryptase activity was present only in mast cells and that all mast cells in the stomach mucosa contained the enzyme. The peptide substrates z-Ala-Ala-Lys-4-methoxy-2-naphthylamide and z-Gly-Pro-Arg-4-methoxy-2-naphthlyamide, which are substrates of choice for demonstrating tryptase in other species, were most effective for demonstrating mouse tryptase. The use of protease inhibitors further indicated that activity present in all mast cells was tryptase. Safranin O did not stain stomach mucosal mast cells, suggesting that the tryptase present in these cells was active in the absence of heparin sulfate proteoglycan.

The influence of nerves on the secretion of immunoglobulin A into submandibular saliva in rats

1. The influence of sympathetic and parasympathetic nerve stimulations on salivary secretion of immunoglobulin A (IgA) was studied in the submandibular glands of anaesthetized rats by stimulating the nerve supplies with bipolar electrodes. 2. Although the flow of saliva from sympathetically stimulated glands was only 23% of that from parasympathetically stimulated glands the output of IgA was over 2-fold greater. This difference was attributable to influences of the nerves on IgA secretion through the epithelial cell polymeric immunoglobulin receptor-mediated pathway, as Western blotting with specific antibodies to IgA and secretory component revealed that secretory IgA (SIgA) dominated in all saliva samples. 3. Study of saliva secreted in sequential periods of nerve stimulation or following rest pauses suggested that SIgA secretion occurred in the absence of stimulation but this was upregulated 2.6- and 6-fold by parasympathetic and sympathetic nerve stimulations, respectively, compared with the calculated unstimulated rate. 4. The IgA content of extensively stimulated glands was 77% of levels in unstimulated contralateral control glands despite a secretion into saliva equivalent to almost 90% of the glandular IgA content. The IgA may be synthesized and secreted by glandular plasma cells at a rate which exceeds demand and/or such synthesis may be upregulated by nerve impulses. 5. The results indicate that salivary secretion of SIgA is upregulated by nerve impulses and that sympathetic nerves induce a greater effect than parasympathetic nerves.

Constitutive secretion of kallikreins in vivo from rat submandibular glands

In parasympathetic saliva from rat submandibular glands the relative proportions of the various tissue kallikreins differ from those in sympathetic saliva. Kallikreins in sympathetic saliva arise from exocytosis of prepackaged granules in granular tubules, so the kallikreins in parasympathetic saliva must come from a non-granular pool, and are likely to be secreted through a constitutive vesicular route. During periods devoid of stimulation in anaesthetised rats, the kallikreins have been found to accumulate progressively in glandular lumina in parasympathetic-like proportions. As this transport of kallikrein into lumina occurs continuously in vivo, independently of any stimulation or any secretion of fluid, it must arise by constitutive vesicular secretion. During parasympathetic stimulation, the kallikreins are secreted into the saliva at a greater rate than in the resting state but their proportions remain the same and the means by which this increase occurs is open to debate. Constitutively secreted true tissue kallikrein (rK1) has been found to have a different molecular form from that in secretory granules. The submandibular glands also contribute to the kallikreins normally circulating in the blood. Serum levels of kallikrein increased equally during either parasympathetic or sympathetic stimulation and were independent of the amounts secreted into the saliva, so are likely to have arisen from constitutive secretion via the basal sides of the cells, morphological evidence for which has been found in the mouse (Penschow & Coghlan, 1993).

Enzyme histochemistry of rat mast cell tryptase

Fixation and staining conditions for rat mast cell tryptase and its histochemical distribution in different rat tissues were investigated. Prostate, skin, lung, gut, stomach and salivary glands were fixed in either aldehyde or Carnoy fixatives and then frozen or embedded in paraffin wax. Preservation of tryptase enzymic activity against peptide substrates required aldehyde fixation and frozen sectioning. Of the peptide substrates examined, z-Ala-Ala-Lys-4-methoxy-2-naphthylamide and z-Gly-Pro-Arg-4-methoxy-2-naphthylamide proved the most effective for the demonstration of tryptase. Double staining by enzyme cytochemistry followed by immunological detection of tryptase showed that, in all tryptase-containing mast cells, the enzyme is at least in part active. Conventional dye-binding histochemistry was used to confirm the identity of mast cells. Aldehyde-fixed mucosal mast cells required a much shorter staining time with Toluidine Blue if tissue sections were washed directly in t-butyl alcohol. Double staining by enzyme cytochemistry and dye binding showed that tryptase is absent from mucosal and subepidermal mast cells, which are also smaller in size and appear to contain fewer granules than connective tissue mast cells. This study demonstrates that rat mast cell tryptase, unlike tryptases in other species, is a soluble enzyme. It is stored in an active form and is absent from some mast cell subpopulations in mucosa, skin and lung.

Protein secretion from rat submandibular acini and granular ducts: effects of exogenous VIP and substance P during parasympathetic nerve stimulation

The influences of exogenous vasoactive intestinal peptide (VIP) and substance P on the release of peroxidase from acini and true tissue kallikrein (rK1) from granular ducts of the rat submandibular gland were studied during continuous parasympathetic stimulation. Parasympathetic nerve impulses caused a moderate flow of saliva (mean +/- SD, 108+/-26 microl/g tissue/min) that had a low protein concentration (174+/-88 microg/ml). The outputs of peroxidase and rK1 were minimal (14.3+/-11.8 pmol DCF/g tissue/min and 6.5+/-3.4 nmol AFC/g tissue/min, respectively). When administered intravenously, VIP had no apparent effect on the overall flow rate, but caused a significant increase in the output of peroxidase; 450% at 1 microg/kg and a further 10-fold increase at 10 microg/kg. In contrast, substance P (1 microg/kg) evoked a marked increase in flow rate (68%), and peroxidase secretion increased only 3-fold. The output of rK1 was unaffected by either VIP or substance P. Our results support the hypothesis that acinar, but not granular duct, protein secretion is evoked by non-adrenergic, non-cholinergic peptides released from parasympathetic nerve terminals.

The enzymic potential of tissue kallikrein (rK1) in rat submandibular saliva depends on whether it was secreted via constitutive or regulated pathways

The enzymic activity and immunoreactivity of rat tissue kallikrein (rK1) secreted at rest by granular duct cells of unstimulated submandibular glands has been compared with that secreted on autonomic nerve stimulation. Although a direct vesicular, constitutive secretory pathway operates for rK1 secretion from granular duct cells of unstimulated and parasympathetically stimulated glands the rK1 was not present in a pro-form and actually showed a greater enzymic activity per unit immunoreactive protein than the granule-derived rK1 in sympathetically evoked saliva. Constitutively secreted rK1 was found to be in a single chain molecular form by reducing SDS gel electrophoresis. In contrast rK1 secreted from the storage granule pool of granular duct cells on sympathetic nerve stimulation was present in much higher amounts and occurred in both one-chain and two-chain forms as revealed by SDS gel electrophoresis under reducing conditions. The lower enzymic potential of rK1 in sympathetically evoked saliva might be accounted for by its conversion to a two-chain form.

Secretory interactions between the sympathetic and parasympathetic innervations of the submandibular gland in the anaesthetized cat

Interactions between the sympathetic and parasympathetic innervations of the submandibular gland have been investigated in the anaesthetized cat. At low frequencies of chorda lingual (parasympathetic) stimulation, simultaneous stimulation of the ascending cervical sympathetic nerve in bursts (20 Hz for 1 s at 10 s intervals) increased the flow of submandibular saliva, but the effect was never more than additive. The output of protein was consistently reduced by simultaneous stimulation of both the sympathetic and parasympathetic innervations, below that evoked by stimulation of either alone. Sympathetic stimulation was more effective than parasympathetic stimulation in promoting the secretion of tissue kallikrein and peroxidase in the submandibular saliva. The output of the latter enzyme, in response to sympathetic stimulation, was significantly reduced by simultaneous stimulation of the parasympathetic innervation at frequencies greater than 1 Hz, but nevertheless exceeded the amount secreted during chorda stimulation alone. Thus, this protocol provided no evidence of synergy between the two divisions of the autonomic nervous system with respect to any submandibular secretory function that was recorded. However, following the administration of a small dose of atropine (2-15 micrograms kg-1 i.v.), sufficient to block secretion during chorda stimulation alone, the flow of saliva, in response to sympathetic stimulation, was potentiated when superimposed on a background of parasympathetic stimulation at all frequencies that were employed. This effect was abolished by larger doses of atropine, indicating that it was dependent upon activation of muscarinic receptors, only some of which could have been blocked by the initial dose.