Intraoral Microbial Metabolism and Association with Host Taste Perception.

Metabolomics has been identified as a means of functionally assessing the net biological activity of a particular microbial community. Considering the oral microbiome, such an approach remains largely underused. While the current knowledge of the oral microbiome is constantly expanding, there are several deficits in knowledge particularly relating to their interactions with their host. This work uses nuclear magnetic resonance spectroscopy to investigate metabolic differences between oral microbial metabolism of endogenous (i.e., salivary protein) and exogenous (i.e., dietary carbohydrates) substrates. It also investigated whether microbial generation of different metabolites may be associated with host taste perception. This work found that in the absence of exogenous substrate, oral bacteria readily catabolize salivary protein and generate metabolic profiles similar to those seen in vivo. Important metabolites such as acetate, butyrate, and propionate are generated at relatively high concentrations. Higher concentrations of metabolites were generated by tongue biofilm compared to planktonic salivary bacteria. Thus, as has been postulated, metabolite production in proximity to taste receptors could reach relatively high concentrations. In the presence of 0.25 M exogenous sucrose, increased catabolism was observed with increased concentrations of a range of metabolites relating to glycolysis (lactate, pyruvate, succinate). Additional pyruvate-derived molecules such as acetoin and alanine were also increased. Furthermore, there was evidence that individual taste sensitivity to sucrose was related to differences in the metabolic fate of sucrose in the mouth. High-sensitivity perceivers appeared more inclined toward continual citric acid cycle activity postsucrose, whereas low-sensitivity perceivers had a more efficient conversion of pyruvate to lactate. This work collectively indicates that the oral microbiome exists in a complex balance with the host, with fluctuating metabolic activity depending on nutrient availability. There is preliminary evidence of an association between host behavior (sweet taste perception) and oral catabolism of sugar.

Salivary Factors that Maintain the Normal Oral Commensal Microflora.

The oral microbiome is one of the most stable ecosystems in the body and yet the reasons for this are still unclear. As well as being stable, it is also highly diverse which can be ascribed to the variety of niches available in the mouth. Previous studies have focused on the microflora in disease-either caries or periodontitis-and only recently have they considered factors that maintain the normal microflora. This has led to the perception that the microflora proliferate in nutrient-rich periods during oral processing of foods and drinks and starves in between times. In this review, evidence is presented which shows that the normal flora are maintained on a diet of salivary factors including urea, lactate, and salivary protein degradation. These factors are actively secreted by salivary glands which suggests these factors are important in maintaining normal commensals in the mouth. In addition, the immobilization of SIgA in the mucosal pellicle indicates a mechanism to retain certain bacteria that does not rely on the bacterial-centric mechanisms such as adhesins. By examining the salivary metabolome, it is clear that protein degradation is a key nutrient and the availability of free amino acids increases resistance to environmental stresses.

Influence of Chemical Species on Polyphenol-Protein Interactions Related to Wine Astringency.

One of the most accepted mechanisms of astringency consists of the interaction between polyphenols and some specific salivary proteins. This work aims to obtain further insights into the mechanisms leading to a modulation of astringency elicited by polyphenols. The effect of the presence of different chemical species (present in food and beverages as food additives) on the polyphenol-protein interaction has been evaluated by means of techniques such as sodium dodecyl sulfate polyacrylamide gel electrophoresis and cell cultures using a cell-based model of the oral epithelium. Results obtained showed that several chemicals, particularly sodium carbonate, seem to inhibit polyphenol binding to salivary proteins and to oral epithelium. These results point out that polyphenol-saliva protein interactions can be affected by some food additives, which can help to better understand changes in astringency perception.

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.

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.

Impact of Obesity on Orthodontic Tooth Movement in Adolescents: A Prospective Clinical Cohort Study.

Obesity is a widespread chronic inflammatory disorder characterized by an increased overall disease burden and significant association with periodontitis. The aim of this prospective clinical cohort study was to investigate the effect of obesity on orthodontic tooth movement. Fifty-five adolescent patients (27 males, 28 females) with a mean (SD) age of 15.1 (1.7) years and mean (SD) body mass index (BMI) of 30.2 (3.5) kg/m2 in obese and 19.4 (2.2) kg/m2 in normal-weight groups were followed from start of treatment to completion of tooth alignment with fixed orthodontic appliances. Primary outcome was time taken to complete tooth alignment, while secondary outcomes included rate of tooth movement and change in clinical parameters (plaque/gingival indices, unstimulated whole-mouth salivary flow rate, gingival crevicular fluid biomarkers). Data collection took place at baseline (start of treatment: appliance placement), 1 h and 1 wk following appliance placement, and completion of alignment. Results were analyzed by descriptive statistics followed by generalized estimating equation regression modeling. There were no significant differences between groups in time taken to achieve tooth alignment (mean [SD] 158.7 [75.3] d; P = 0.486). However, at 1 wk, initial tooth displacement was significantly increased in the obese group ( P < 0.001), and after adjusting for confounders, obese patients had a significantly higher rate of tooth movement compared with normal-weight patients (+0.017 mm/d; 95% confidence interval, 0.008-0.025; P < 0.001) over the period of alignment. Explorative analyses indicated that levels of the adipokines leptin and resistin, the inflammatory marker myeloperoxidase (MPO), and the cytokine receptor for nuclear factor kappa-B ligand (RANKL) were significantly different between obese- and normal-weight patients and associated with observed rates of tooth movement. This represents the first prospective data demonstrating a different response in obese patients compared with normal-weight patients during early orthodontic treatment. These differences in the response of periodontal tissues to orthodontic force in the presence of obesity have potential short- and long-term clinical implications.

Changes in Saliva Rheological Properties and Mucin Glycosylation in Dry Mouth.

Saliva is vital for the maintenance of normal oral physiology and mucosal health. The loss of salivary function can have far-reaching consequences, as observed with dry mouth, which is associated with increased orodental disease, speech impairment, dysphagia, and a significant negative effect on quality of life. The timely diagnosis of oral dryness is vital for the management of orodental disease and any associated often-undiagnosed systemic disease (e.g., Sjögren syndrome). Our aim was to investigate differences in mucin glycoproteins and saliva rheological properties between sufferers and nonsufferers of dry mouth in order to understand the relationship between saliva composition, rheological properties, and dryness perception and provide additional potential diagnostic markers. All patients exhibited objective and subjective oral dryness, irrespective of etiology. Over half of the patients (n = 20, 58.8%) had a saliva secretion rate above the gland dysfunction cutoff of 0.1 mL/min. Mucin (MUC5B and MUC7) concentrations were generally similar or higher in patients. Despite the abundance of these moisture-retaining proteins, patients exhibited reduced mucosal hydration (wetness) and significantly lower saliva spinnbarkeit (stringiness), suggesting a loss of the lubricating and retention/adhesion properties of saliva, which, at least partially, are associated with mucin glycoproteins. Over 90% of patients with dry mouth (DMPs) consistently had unstimulated whole mouth saliva (UWMS) spinnbarkeit below the proposed normal cutoff (10 mm). Further analysis of mucins revealed the reduced glycosylation of mucins in DMPs compared to healthy controls. Our data indicate that UWMS mucin concentrations are not reduced in dry mouth but that the mucin structure (glycosylation) is altered. UWMS from DMPs had reduced spinnbarkeit, the assessment of which, in conjunction with sialometry, could improve sensitivity for the diagnosis of dry mouth. Additionally, it may be useful to take into consideration the altered mucin glycosylation and saliva rheological properties when designing synthetic or purified mucins for saliva substitutes and dry mouth therapy.

Rapamycin delays salivary gland atrophy following ductal ligation.

Salivary gland atrophy is a frequent consequence of head and neck cancer irradiation therapy but can potentially be regulated through the mammalian target of rapamycin (mTOR). Excretory duct ligation of the mouse submandibular gland provokes severe glandular atrophy causing activation of mTOR. This study aims to discover the effects of blocking mTOR signaling in ligation-induced atrophic salivary glands. Following 1 week of unilateral submandibular excretory duct ligation: gland weights were significantly reduced, 4E-BP1 and S6rp were activated, and tissue morphology revealed typical signs of atrophy. However, 3 days following ligation with rapamycin treatment, a selective mTOR inhibitor, gland weights were maintained, 4E-BP1 and S6rp phosphorylation was inhibited, and there were morphological signs of recovery from atrophy. However, following 5 and 7 days of ligation and rapamycin treatment, glands expressed active mTOR and showed signs of considerable atrophy. This evidence suggests that inhibition of mTOR by rapamycin delays ligation-induced atrophy of salivary glands.

Concentration of salivary protective proteins within the bound oral mucosal pellicle.

OBJECTIVES: To study which salivary proteins form the protective bound mucosal pellicle and to determine the role of transglutaminase in pellicle development. MATERIALS AND METHODS: Oral epithelial cells were collected and underwent washes of different strengths, followed by homogenisation. SDS-PAGE, western blotting, IgA ELISAs and amylase activity assays were completed on cell homogenates and compared to saliva samples to confirm which salivary proteins were bound to cell surfaces. RESULTS: Salivary mucins, MUC5B and MUC7, were strongly retained on the oral epithelial cell surface. Other bound proteins including cystatin S, carbonic anhydrase VI, secretory component and IgA could be washed off. IgA was present in concentrated levels in the bound mucosal pellicle compared to amounts in saliva. Amylase, one of the most abundant proteins present in saliva, showed minimal levels of binding. Transglutaminase 3 presence was confirmed, but proteins that it catalyses cross-links between, statherin and proline-rich proteins, showed minimal presence. CONCLUSION: Some protective salivary proteins including mucins and IgA become concentrated on oral surfaces in the bound mucosal pellicle, through specific interactions. Concentration of mucins would contribute to lubrication to prevent abrasion damage to soft tissues, whilst increased IgA could create an 'immune reservoir' against mucosal infection.

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.

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.

A physiological model of tea-induced astringency.

The mechanism by which solutions containing polyphenols are perceived as astringent is not clearly understood. Salivary proline-rich proteins and histatins are products of salivary glands and rapidly bind polyphenols - thought to be the main astringent compound in such as tea and wine. However it is unclear how this interaction leads to the altered oral mouthfeel known as astringency which is characterised by a dry, puckered feeling all around the mouth. To determine the role of saliva in the perception of astringency a protocol was used to decrease the volume of saliva from the mouth (by washing with water) and then by chewing to increase the volume of saliva above resting levels. Following each of these conditions subjects tasted the same solution of black tea and were asked to rate the relative astringency. Compared to the astringency rating of black tea at rest the majority of subjects (10 out of 15) perceived an increase in astringency following washing the mouth with water. Most subjects then perceived a decrease in astringency following chewing compared to the previous state. In all subjects a reduction in salivary proteins was detected following water washout and an increase above resting levels detected following chewing although there was no change in oral mucosal wetness. A separate experiment revealed several of the proteins interacting following the water washout were salivary in origin. We conclude that salivary proteins in solution inhibit the mouthfeeling of astringency which is mediated, at least in part, by salivary proteins adhered to buccal mucosal cells.

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 microl min(-1) g(-1)vs 177 +/- 11 microl 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 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 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).