Effect of lipids on the lactic acid retardation capacity of tooth enamel and cementum pellicles formed in vitro from saliva of caries-resistant and caries-susceptible human adults

Multiomics analysis reveals the genetic and metabolic characteristics associated with the low prevalence of dental caries

Background

Despite poor oral hygiene, the Baiku Yao (BKY) ethnic group in China presents a low prevalence of dental caries, which may be related to genetic susceptibility. Due to strict intra-ethnic marriage rule, this ethnic has an advantage in studying the interaction between genetic factors and other regulatory factors related to dental caries.

Methods

Peripheral blood from a caries-free adult male was used for whole genome sequencing, and the BKY assembled genome was compared to the Han Chinese genome. Oral saliva samples were collected from 51 subjects for metabolomic and metagenomic analysis. Multiomics data were integrated for combined analysis using bioinformatics approaches.

Results

Comparative genomic analysis revealed the presence of structural variations in several genes associated with dental caries. Metabolomic and metagenomic sequencing demonstrated the caries-free group had significantly higher concentration of antimicrobials and higher abundance of core oral health-related microbiota. The functional analysis indicated that cationic antimicrobial peptide resistance and the lipopolysaccharide biosynthesis pathway were enriched in the caries-free group.

Conclusions

Our study provided new insights into the specific regulatory mechanisms that contribute to the low prevalence of dental caries in the specific population and may provide new evidence for the genetic diagnosis and control of dental caries.

An immuno-lipidomic signature revealed by metabolomic and machine-learning approaches in labial salivary gland to diagnose primary Sjögren's syndrome

Introduction

Assessing labial salivary gland exocrinopathy is a cornerstone in primary Sjögren's syndrome. Currently this relies on the histopathologic diagnosis of focal lymphocytic sialadenitis and computing a focus score by counting lym=phocyte foci. However, those lesions represent advanced stages of primary Sjögren's syndrome, although earlier recognition of primary Sjögren's syndrome and its effective treatment could prevent irreversible damage to labial salivary gland. This study aimed at finding early biomarkers of primary Sjögren's syndrome in labial salivary gland combining metabolomics and machine-learning approaches.

Methods

We used a standardized targeted metabolomic approach involving high performance liquid chromatography coupled with mass spectrometry among newly diagnosed primary Sjögren's syndrome (n=40) and non- primary Sjögren's syndrome sicca (n=40) participants in a prospective cohort. A metabolic signature predictive of primary Sjögren's syndrome status was explored using linear (logistic regression with elastic-net regularization) and non-linear (random forests) machine learning architectures, after splitting the data set into training, validation, and test sets.

Results

Among 126 metabolites accurately measured, we identified a discriminant signature composed of six metabolites with robust performances (ROC-AUC = 0.86) for predicting primary Sjögren's syndrome status. This signature included the well-known immune-metabolite kynurenine and five phospholipids (LysoPC C28:0; PCaa C26:0; PCaaC30:2; PCae C30:1, and PCaeC30:2). It was split into two main components: the first including the phospholipids was related to the intensity of lymphocytic infiltrates in salivary glands, while the second represented by kynurenine was independently associated with the presence of anti-SSA antibodies in participant serum.

Conclusion

Our results reveal an immuno-lipidomic signature in labial salivary gland that accurately distinguishes early primary Sjögren's syndrome from other causes of sicca symptoms.

Functional biomedical materials derived from proteins in the acquired salivary pellicle

In the oral environment, the acquired salivary pellicle (ASP) on the tooth surface comprises proteins, glycoproteins, carbohydrates, and lipids. The ASP can specifically and rapidly adsorb on the enamel surface to provide effective lubrication, protection, hydration, and remineralisation, as well as be recognised by various bacteria to form a microbial biofilm (plaque). The involved proteins, particularly various phosphoproteins such as statherins, histatins, and proline-rich proteins, are vital to their specific functions. This review first describes the relationship between the biological functions of these proteins and their structures. Subsequently, recent advances in functional biomedical materials derived from these proteins are reviewed in terms of dental/bone therapeutic materials, antibacterial materials, tissue engineering materials, and coatings for medical devices. Finally, perspectives and challenges regarding the rational design and biomedical applications of ASP-derived materials are discussed.

Modification of the Lipid Profile of the Initial Oral Biofilm In Situ Using Linseed Oil as Mouthwash

Lipids are of interest for the targeted modification of oral bioadhesion processes. Therefore, the sustainable effects of linseed oil on the composition and ultrastructure of the in situ pellicle were investigated. Unlike saliva, linseed oil contains linolenic acid (18:3), which served as a marker for lipid accumulation. Individual splints with bovine enamel slabs were worn by five subjects. After 1 min of pellicle formation, rinses were performed with linseed oil for 10 min, and the slabs' oral exposure was continued for up to 2 or 8 h. Gas chromatography coupled with electron impact ionization mass spectrometry (GC-EI/MS) was used to characterize the fatty acid composition of the pellicle samples. Transmission electron microscopy was performed to analyze the ultrastructure. Extensive accumulation of linolenic acid was recorded in the samples of all subjects 2 h after the rinse and considerable amounts persisted after 8 h. The ultrastructure of the 2 h pellicle was less electron-dense and contained lipid vesicles when compared with controls. After 8 h, no apparent ultrastructural effects were visible. Linolenic acid is an excellent marker for the investigation of fatty acid accumulation in the pellicle. New preventive strategies could benefit from the accumulation of lipid components in the pellicle.

Association of Salivary Lipids and Early Childhood Caries in an Indian Subpopulation: A Preliminary Study

Aim: This preliminary study aimed to estimate and correlate the relationship between salivary flow rate and levels of salivary triglycerides, cholesterol and total lipids in children with and without early childhood caries. Study design: Ninety children aged 3 - 6 years were divided into three groups of 30 each based on their decayed missing filled tooth (dmft) score, group I (dmft score = 0), group II (dmft score ≥4 and ≤ 9) and group III (dmft scores ≥ 10). Whole unstimulated saliva was collected in a sterile graduated cup over a period of 5 minutes and was quantitatively analyzed for levels of salivary triglycerides, cholesterol and total lipids. Data obtained was subjected to statistical analysis by one way ANOVA, Post-Hoc tukey and Pearson's correlation test. Results: Salivary flow rate was 1.20±0.36, 1.01±0.37 and 0.86±0.31 ml/min in group I, II and III respectively. The mean levels of salivary triglycerides in group I, II and III was 3.57±0.43mg/ml, 6.11±1.70mg/ml and 6.03±1.73 mg/ml, respectively. The mean levels of salivary total lipids were higher in group II and III, ie 22.51±2.87 mg/ml and 22.68±2.54 mg/ml respectively. The mean level of salivary cholesterol was highest in group III (8.03±2.91 mg/ml). Salivary triglycerides and total lipids showed a significant positive correlation with dmft scores of children (p≤ 0.001). Salivary cholesterol also had a positive association with dental caries experience of children but was not significant. There was a negative correlation between salivary flow rate and levels of salivary triglycerides, cholesterol and total lipids. Conclusion: Children with ECC (group II and III) had lower salivary flow rate and higher levels of salivary triglycerides and total lipids compared to caries free children (group I). Levels of salivary cholesterol did not differ between caries free and children with ECC.

Oil droplet formation on pellicle covered tooth surfaces studied with environmental scanning electron microscopy

Lipophilic components are known to modulate the process of bioadhesion on the tooth surface. However, the presence of lipid droplets at the acquired pellicle under oral conditions has not been demonstrated, yet. The purpose of the present study was to establish a method for direct visualisation of lipids on the surface of hydrated, pellicle covered tooth samples by environmental scanning electron microscopy (ESEM), and to use this technique for studying the effects of rinsing with edible oils on the acquired pellicle under in vivo conditions. In situ pellicle formation was performed by 3 min exposure of enamel and dentin specimens in the oral cavity of volunteers. Subsequently, the volunteers rinsed in vivo with safflower oil or linseed oil for 30 s, and the specimens were further carried intraorally for periods from 0 min up to several hours. After intraoral exposure the specimens were treated by osmium tetroxide vapour, and were subsequently analysed by ESEM. This technique was capable to directly visualise the presence of lipid droplets at the pellicle's surface under hydrated conditions. ESEM analyses revealed that surface bound nano- and micro-sized lipid droplets were present at the acquired pellicle's surface even several hours after rinsing with edible oils indicating that these droplets had tightly adhered to the pellicle surface. Pellicle modification by edible oil rinsing as demonstrated in the present study might have the potential to be beneficial as an adjunct in dental prophylaxis.

Glycan recognition at the saliva - oral microbiome interface

The mouth is a first critical interface where most potentially harmful substances or pathogens contact the host environment. Adaptive and innate immune defense mechanisms are established there to inactivate or eliminate pathogenic microbes that traverse the oral environment on the way to their target organs and tissues. Protein and glycoprotein components of saliva play a particularly important role in modulating the oral microbiota and helping with the clearance of pathogens. It has long been acknowledged that glycobiological and glycoimmunological aspects play a pivotal role in oral host-microbe, microbe-host, and microbe-microbe interactions in the mouth. In this review, we aim to delineate how glycan-mediated host defense mechanisms in the oral cavity support human health. We will describe the role of glycans attached to large molecular size salivary glycoproteins which act as a first line of primordial host defense in the human mouth. We will further discuss how glycan recognition contributes to both colonization and clearance of oral microbes.

Effect of Mouthrinses containing Olive Oil, Fluoride, and Their Combination on Enamel Erosion: An in vitro Study

AIM

The aim of the study was to evaluate the effect of mouth-rinses containing olive oil, fluoride, and their combination on enamel erosion.

MATERIALS AND METHODS

An in vitro study of 45 enamel specimens, which were prepared from 45 extracted teeth, was employed. Each specimen was subjected to 10 alternative demineralization and remineralization cycles. Remineralizing cycle includes 5 minutes exposure with one of the mouthrinse, and demineralizing cycle includes 3 minute exposure to 1% citric acid. Mean surface roughness (Ra) was measured from surfometry before and after cycles. Statistical tests used were Student's unpaired t-test and one-way analysis of variance (ANOVA), followed by Tukey's post hoc test.

RESULTS

Among the three mouthrinses, Listerine and Xerostom showed maximum protection against erosion on enamel. The 2% olive oil mouthrinse showed the least protection against erosion on enamel.

CONCLUSION

The study indicated that the Listerine and Xerostom mouthrinses are valuable preventive measures.

CLINICAL SIGNIFICANCE

Mouthrinses are effective for lessening erosive demineralization and in aggregating remineralization of tooth surfaces which are the important factors to prevent enamel erosion.

A comprehensive method for determination of fatty acids in the initial oral biofilm (pellicle)

The acquired pellicle is a tenacious organic layer covering the surface of teeth, protecting the underlying dental hard tissues. Lipids account for about one quarter of the pellicle's dry weight and are assumed to be of considerable importance for their protective properties. Nevertheless, only preliminary information is available about the nature of lipids in the pellicle. Gas chromatography coupled with electron impact ionization mass spectrometry was used to establish a convenient analytical protocol in order to obtain a qualitative and quantitative characterization of a wide range of FAs (C(12)-C(22)). In situ biofilm formation was performed on bovine enamel slabs mounted on individual splints carried by 10 subjects. A modified Folch extraction procedure was adopted to extract the lipids from the detached pellicle, followed by transesterification to fatty acid methyl esters using methanol and concentrated hydrochloric acid. Tridecanoic and nonadecanoic acid were used as internal standards suitable and reliable for robust, precise and accurate measurements. The present study demonstrates, for the first time, a procedure based on a combination of innovative specimen generation and convenient sample preparation with sensitive GC-MS analysis for the determination of the fatty acid profile of the initial oral biofilm.

Do edible oils reduce bacterial colonization of enamel in situ?

OBJECTIVE

Edible oils are an empiric approach for the prevention of oral diseases. The present in situ study investigated the effect of edible oils on initial bacterial colonization of enamel surfaces.

METHODS AND MATERIALS

Initial biofilm formation was performed on enamel specimens mounted on maxillary splints and carried by eight subjects. After 1 min of pellicle formation, rinses with safflower oil, olive oil and linseed oil were performed for 10 min. Application of chlorhexidine for 1 min served as positive control. Afterwards, the slabs were carried for 8 h overnight. Samples carried for 8 h without any rinse served as negative controls. The amount of adherent bacteria was determined by DAPI staining (4',6-diamidino-2-phenylindole) and live-dead staining (BacLight). Additionally, determination of colony forming units was performed after desorption of the bacteria. TEM evaluation was carried out after application of the rinses.

RESULTS

The number of adherent bacteria on control samples was 6.1 ± 8.1 × 10(5)/cm(2) after 8 h (DAPI). Fluorescence microscopic data from DAPI staining and live-dead staining as well as from the determination of CFU revealed no significant effects of rinsing with oils on the amount of adherent bacteria compared to the non-rinsed control samples. However, with chlorhexidine a significant reduction in the number of bacteria by more than 85 % was achieved (DAPI, chlorhexidine: 8.2 ± 17.1 × 10(4)/cm(2)). The ratio of viable to dead bacteria was almost equal (1:1) irrespective of the rinse adopted as recorded with BacLight. TEM indicated accumulation of oil micelles at the pellicle's surface and modification of its ultrastructure.

CONCLUSION

Rinses with edible oils have no significant impact on the initial pattern and amount of bacterial colonization on enamel over 8 h.

CLINICAL RELEVANCE

Rinses with edible oils cannot be recommended for efficient reduction of oral biofilm formation.

Effect of Artificial Saliva on the Apatite Structure of Eroded Enamel

Citric acid-induced changes in the structure of the mineral component of enamel stored in artificial saliva were studied by attenuated total reflectance infrared spectroscopy as well as complementary electron probe microanalysis and scanning electron microscopy. The results indicate that the application of artificial saliva for several hours (the minimum time period proved is 4 h) leads to slight, partial recovering of the local structure of eroded enamel apatite. However, artificial saliva surrounding cannot stop the process of loosening and breaking of P–O–Ca atomic linkages in enamel subjected to multiple citric acid treatments. Irreversible changes in the atomic bonding within 700 nm thick enamel surface layer are observed after three times exposure for 1 min to aqueous solution of citric acid having a pH value of 2.23, with a 24-hour interval between the individual treatments. The additional treatment with basic fluoride-containing solutions (1.0% NaF) did not demonstrate a protective effect on the enamel apatite structure per se.

Lipid patterns in the saliva of smoking young adults

Salivary lipids are important for the maintenance of oral cavity health. Elevated salivary lipid levels are associated with an increase of caries incidence, plaque development, calculus formation and periodontal disease. However, the regulation of lipid salivary levels is scarcely known. Cigarette smoke is considered a risk factor for oral cavity diseases. We study how cigarette smoke may affect the secretion of salivary lipids. To this purpose, we determine the salivary levels of cholesterol and of glycerolipids in saliva sampled from smokers and non-smokers at various times of day. We observe an increase of glycerophospholipid and a decrease of cholesterol levels in the smokers' saliva collected at 10 p.m. On the other hand, unsaturated fatty acids in chief phospholipids of saliva are lower in smokers at 7 a.m. Therefore, for the first time, we demonstrate that cigarette smoke induces variations of saliva lipid pattern in young people even moderately smoking.

Effect of olive oil and an olive-oil-containing fluoridated mouthrinse on enamel and dentin erosion in vitro

OBJECTIVE

The study aimed to analyse the impact of olive oil and an olive-oil-containing fluoridated mouthrinse on enamel and dentin erosion.

MATERIAL AND METHODS

Bovine enamel and dentin specimens were submitted to 10 alternating demineralization and remineralization cycles each consisting of 5 min pretreatment with the test solutions, i.e. distilled water as negative control, 100% olive oil, 2% olive oil emulsion, 2% olive-oil-containing mouthrinse (Xerostom), acidic 13.2 mmol x l(-1) (250 ppm) fluoride solution as positive control, storage in artificial saliva (30 min), demineralization in citric acid (3 min, pH 2.3) and again storage in artificial saliva (60 min). Each group contained 10 enamel and dentin samples. Enamel and dentin loss was analyzed by profilometry after 10 cycles.

RESULTS

Treatment with 100% olive oil was not effective in reducing enamel and dentin loss. Application of 2% olive oil or the olive-oil-containing mouthrinse also showed protection against erosion, but to a lesser degree compared to the positive control.

CONCLUSION

Olive oil offered protection against enamel and dentin erosion when applied as 2% emulsion or 2% olive-oil-containing mouthrinse, but is not effective when applied as pure oil (100%). However, 2% olive oil emulsion is less effective in reducing erosion compared to the acidic 13.2 mol x l(-1) fluoride solution.

Phospholipid Profiles in the Salivary Glands of Rats of Different Ages

It has been reported that diabetes and Sjögren's syndrome patients exhibit variations in the amount of salivation and in the lipid components in saliva and salivary glands. We examined whether lipid compositions, especially phospholipid ones in the salivary glands of rats varied with aging. We analyzed phospholipid and fatty acid compositions in the salivary glands of young (5 to 6 weeks), adult (20 weeks), and old (50 weeks) rats and biochemical components in their blood. The aging (adult and old) rats had higher triacylglycerol, total lipid, total cholesterol and glucose contents in the plasma than the young one. The aging ones also had higher total lipid contents in the major salivary glands (parotid, submandibular and sublingual glands). They had higher wet weights of the major salivary glands and epididymal fat pads than the young ones, but had lower ratios of the major salivary glands to body weight. All of them had high phospholipid contents in the parotid and submandibular glands as compared to sublingual gland, but the aging ones had lower percentage of phospholipid contents of all salivary glands. Phosphatidylcholine and phosphatidylethanolamine were predominant among the phospholipids in the major salivary glands, and little difference was observed in phospholipid composition among the three groups. Palmitic and stearic acids (saturated acids), and linoleic, oleic and arachidonic acids (unsaturated acids) were major components of fatty acids of phospholipids in the major salivary glands. The aging ones had higher linoleic and lower arachidonic acid contents in the glands than the young one. In summary, the aging rats had higher total lipid contents than the young ones and had lower phospholipid contents of the major salivary glands. The n-6 fatty acid contents differed between aging and young ones. The results suggest that phospholipids in the major salivary glands change with the development of rat.

Enzymes in the acquired enamel pellicle

The acquired pellicle is a biofilm, free of bacteria, covering oral hard and soft tissues. It is composed of mucins, glycoproteins and proteins, among which are several enzymes. This review summarizes the present state of research on enzymes and their functions in the dental pellicle. Theoretically, all enzymes present in the oral cavity could be incorporated into the pellicle, but apparently enzymes are adsorbed selectively onto dental surfaces. There is clear evidence that enzymes are structural elements of the pellicle. Thereby they exhibit antibacterial properties but also facilitate bacterial colonization of dental hard tissues. Moreover, the immobilized enzymes are involved in modification and in homeostasis of the salivary pellicle. It has been demonstrated that amylase, lysozyme, carbonic anhydrases, glucosyltransferases and fructosyltransferase are immobilized in an active conformation in the pellicle layer formed in vivo. Other enzymes, such as peroxidase or transglutaminase, have been investigated in experimental pellicles. Despite the depicted impact of enzymes on the formation and function of pellicle, broader knowledge on their properties in the in vivo-formed pellicle is required. This might be beneficial in the development of new preventive and diagnostic strategies.

Protective effect of the in situ formed short-term salivary pellicle

Salivary pellicle, as previously investigated, protects the enamel surface after certain processes of maturation against the influence of acidic agents. The aim of the present study was to investigate the protective effect of the short-term salivary pellicle formed in situ over periods of 3, 60 and 120 min. Six human volunteers used intraoral acrylic splints with bovine enamel samples fixed at the buccal and palatal sites of the maxillary first molars and second premolars. Enamel specimens (n = 252) with and without pellicle were immersed for 60 s in 1.0% citric acid solution under agitation. Knoop surface hardness (KHN) of uneroded polished enamel was measured as a baseline and estimated immediately after erosive treatment reflecting the microhardness loss (DeltaKHN). The amounts of calcium dissolved from the eroded enamel surface were analysed by atomic absorption spectroscopy and scored in mg/l per 10 mm2 of enamel surface area. In addition, the scanning electron microscope was used for the micromorphological examination of the erosive alterations of the enamel surface. The average microhardness loss values after erosion of the enamel samples with buccally/palatally formed pellicle layers were measured as 139.1/144.9 DeltaKHN for 3 min pellicle, 145.9/146.9 DeltaKHN for 60 min pellicle and 141.7/138.6 DeltaKHN for 120 min pellicle. Calcium release values from the specimens with buccal/palatal pellicles were amounted to 15.0/14.9, 16.5/15.9 and 15.3/17.4 mg/l per 10 mm2 for 3, 60 and 120 min-old pellicles, respectively. No significant differences were related to the pellicle formation time and intraoral site (buccal or palatal) in all tested series (ANOVA, P < 0.05). However, significant protection of the enamel surface provided by the pellicle layer was observed on all pellicle-covered surfaces if compared to the non-covered enamel samples (calcium release: 25.6 mg/l per 10 mm2; microhardness loss 187.0 DeltaKHN). These data were in accordance with the morphologic alterations caused by citric acid on the pellicle-covered and pellicle non-covered specimens. It could be concluded that salivary pellicle formed in situ within a period of 3 min offers protection of enamel against citric acid. However, pellicle does not completely inhibit the erosive action of citric acid under the conditions of the present study.

Salivary mucins in oral mucosal defense

1. Salivary mucins are well recognized as an important factor in the preservation of the health of the oral cavity. These large glycoproteins play a major role in the formation of protective coatings covering tooth enamel and oral mucosa, which act as a dynamic functional barrier capable of modulating the untoward effects of oral environment, and are of significance to the processes occurring within the epithelial perimeter of mucosal defense. 2. Based on macromolecular characteristics, the mucins in saliva fall into high (> 1000 kDa) and low (200-300 kDa) molecular weight forms. The two forms, although differ with respect to bacterial clearance ability, display virtually identical carbohydrate chain make-up, ranging in size from 3 to 16 sugar units. 3. Of the two mucin forms, the low molecular weight form more efficient in bacterial aggregation, predominates in saliva and oral mucosal mucus coat of caries-resistant individuals, while the level of the high molecular weight form is higher in caries-susceptible subjects. The saliva of caries-resistant individuals also exhibits greater activity of protease capable of conversion of the high molecular weight mucin to the low molecular weight form. 4. The bacterial aggregating activity of salivary mucins appears to be associated with sulfomucins rather than sialomucins. While the removal of sialic acid causes only partial loss in mucin aggregating capacity, a complete loss in the bacterial aggregating activity occurs following mucin desulfation. 5. The mucins in oral mucosal mucus coat interact with the epithelial surfaces through specific membrane receptors. This interaction apparently involves the carbohydrate moiety of mucin molecule and may be rendered vulnerable to disruption by opportunistic bacteria colonizing the oral mucosa. 6. Salivary sulfo- and sialomucins actively participate in the modulation of the oral mucosal calcium channel activity through the inhibition of EGF-stimulated channel protein tyrosine phosphorylation. This function of salivary mucins is of paramount importance to mucosal calcium homeostasis.

Lipids in human saliva

A simple and reproducible method of determining the quality and quantity of neutral lipids in human saliva was tested. Parotid, submandibular and whole stimulated saliva were collected from 10 healthy adults. The lipids were extracted by the Folch method. A special method for extraction of glycolipids was also tested but gave no additional recovery. Thin-layer chromatography was used for separating the different lipid classes. The concentrations of total lipids in parotid, submandibular and whole stimulated saliva were 0.2, 0.9 and 1.3 mg/dl, respectively. Cholesteryl esters, cholesterol, triglycerides, diglycerides, monoglycerides and free fatty acids accounted for 96-99 percent of the total salivary lipids. Thus, polar lipids such as phospholipids contributed only a minor fraction, indicating that the lipids are not primarily of membrane origin. Ultracentrifugation of saliva samples at d = 1.21 g ml(-1) showed that the salivary lipids did not float like blood plasma lipoproteins. Therefore, they must be in a different state of aggregation from lipids in blood or lymph. No significant lipase activity of the type that acts on plasma lipoproteins was found in parotid or submandibular saliva. The content of free fatty acids and partial glycerides was high.

Role of adrenergic and cholinergic mediators in salivary phospholipids secretion

The influence of adrenergic and cholinergic mediators on phospholipid secretion in rat sublingual salivary gland cells maintained in the presence of [3H]choline was investigated. The secretion of [3H]choline-containing phospholipids over 30 min period averaged 1.93% of the total cellular labeled phospholipids in the absence of any mediator, and was enhanced by beta-adrenergic agonist, isoproterenol, to a greater extent than the cholinergic agonists, pilocarpine and carbachol. A 2.9-fold increase in phospholipid secretion occurred with isoproterenol, while pilocarpine and carbachol evoked only 1.3-fold increase. The effect of isoproterenol was inhibited by alprenolol and that of pilocarpine and carbachol by atropine. In contrast to pilocarpine and carbachol, the enhanced phospholipid secretion due to isoproterenol was accompanied by an increase in cAMP concentration. The secretion of phospholipids was also stimulated by dibutyryl-cAMP and the protein kinase C activator, phorbol myristate acetate, but not by 4 alpha-phorbol 12,13-didecanoate which does not activate protein kinase C. Furthermore, the effects of dibutyryl-cAMP and phorbol myristate acetate were additive. The phospholipids secreted in response to isoproterenol exhibited a 52% decrease in lysophosphatidylcholine, while those secreted in response to pilocarpine and carbachol showed a 21-23% lower content of phosphatidylcholine, and were enriched in lysophosphatidylcholine (2.6-2.8-fold) and sphingomyelin (1.5-1.6-fold). The results indicate that salivary phospholipid secretion remains mainly under beta-adrenergic regulation, while the phospholipid makeup of the secretion is under cholinergic control.