Prostaglandin synthesis by murine salivary glands

Enhancement of carbachol-induced amylase secretion in parotid glands from rats with experimental periodontitis

OBJECTIVE

In a previous study we observed that parotid glands from rats with experimental periodontitis showed an increase in basal amylase release as a result of an increase in cAMP accumulation induced by PGE(2) production. The aim of this work was to study whether this change in amylase release influences the secretory effect of carbachol.

DESIGN

Experimental periodontitis was induced through placing a black thread around the cervix of the two lower first molars. Experiments were done 22 days after ligature induced periodontitis. Amylase release was evaluated in vitro and determined using a colorimetric method which uses starch as substrate.

RESULTS

The effect of carbachol was increased in parotid glands from periodontitis rats. The effect of 10(-6)M carbachol was inhibited by 4-DAMP (10(-6)M), U-73122 (5 × 10(-6)M) and trifluoperazine (5 × 10(-6)M) in both groups. No changes were observed in the binding sites and affinity in parotid membranes from rats with experimental periodontitis. The inhibition of the adenylyl cyclase and the cyclooxygenase induced a right shift of the carbachol concentration-response curve in periodontitis group whilst the opposite effect was observed in control group in the presence of db-cAMP and PGE(2).

CONCLUSIONS

Parotid glands from rats with experimental periodontitis release more amylase in response to carbachol suggesting an interaction between Ca(2+) and cAMP in the fusion/exocytosis step of secretory vesicles.

Experimental periodontitis induces a cAMP-dependent increase in amylase activity in parotid glands from male rats

It is known that subjects with periodontitis show enhanced amylase concentration in saliva. Our purpose was to analyze the release of amylase in parotid glands from rats with experimental periodontitis and controls. We present evidence that periodontitis induces an increase in resting amylase activity and release without changes in isoproterenol-induced amylase secretion. Changes in amylase were reverted by the inhibition of the adenylyl cyclase by SQ 22536, the cyclooxygenase type 1 by FR 122047 and by blocking the vasoactive intestinal peptide (VIP) receptor with VIP 6-28. Parotid glands from rats with periodontitis showed an increase in cAMP levels that was also reverted in the presence of SQ 22536, FR 122047 and VIP 6-28. We concluded that both PGE(2) and VIP are produced in parotid glands from rats with periodontitis and, by activating their own receptors in acinar cells, induce cAMP accumulation leading to an increase in amylase basal secretion.

Decreased levels of salivary prostaglandin E2 and epidermal growth factor in recurrent aphthous stomatitis

Prostaglandin E2 and epidermal growth factor are two important cytoprotective compounds in saliva. This study investigated their salivary levels in controls and individuals with minor recurrent aphthous stomatitis. The development of recurrent aphthous stomatitis was divided into three stages: (1) early active stage (mucosal redness); (2) active stage (mucosal ulceration); (3) convalescent stage. Unstimulated mixed saliva was collected from each volunteer. Salivary prostaglandin E2 and epidermal growth factor concentrations were determined by radioimmunoassay. Their levels (mean +/- SEM) were significantly lower during the active stage of ulceration as compared to the control: (a) for prostaglandin E2, 200 +/- 55 versus 73 +/- 11 pg/mg salivary protein (p < 0.01), 447 +/- 123 versus 112 +/- 19 pg/ml saliva (p < 0.01), 215 +/- 30 versus 63 +/- 12 pg/min salivary flow (p < 0.01), control (n = 12) versus active stage (n = 15); (b) for epidermal growth factor, 1.09 +/- 0.17 versus 0.67 +/- 0.17 ng/mg salivary protein (p < 0.05); 2.51 +/- 0.53 versus 0.84 +/- 0.19 pg/ml saliva (p < 0.05), 1.24 +/- 0.26 versus 0.41 +/- 0.09 pg/min salivary flow (p < 0.05), control (n = 12) versus active stage (n = 12). Salivary prostaglandin E2 and epidermal growth factor showed stage-dependent alterations during the development of the stomatitis. The prostaglandin E2 concentration decreased significantly during the active stage of ulceration, and then increased significantly during the convalescent stage. However, the recovery of salivary epidermal growth factor after the ulceration was slower than that of the prostaglandin E2. It is suggested that the diminution of prostaglandin E2 and epidermal growth factor in the saliva may be associated with the ulcer development.

Substrate specificity of microsomal 1-acyl-sn-glycero-3-phosphoinositol acyltransferase in rat submandibular gland for polyunsaturated long-chain acyl-CoAs

Microsomal 1-acyl-sn-glycero-3-phosphoinositol (1-acyl-GPI) acyltransferase in the rat submandibular gland showed the highest specific activities for eicosanoid-related polyunsaturated acyl-CoAs, such as arachidonoyl-, bishomo-gamma-linolenoyl- and 5,8,11,14,17-eicosapentaenoyl-CoAs, with low Km values. High activities were also obtained with acyl-CoAs having long (more than 14 carbon atoms) and n - 6 unsaturated (more than 3 double bonds) acyl chains. This enzyme also utilized acyl-CoAs having trans-unsaturated or branched chains, but not short-chains, as substrates, although the activity levels for trans-unsaturated acyl-CoAs were lower than those for cis-unsaturated acyl-CoAs. Chronic administration of isoproterenol induced decreases of this enzyme activity and the content of arachidonic, bishomo-gamma-linolenic and 5,8,11,14,17-eicosapentaenoic acids at the sn-2 position of phosphatidylinositol. These results suggest that enrichment of arachidonic acid in the sn-2 position of phosphatidylinositol is established by the high specificity and affinity of 1-acyl-GPI acyltransferase for arachidonoyl-CoA. On the other hand, the low level of bishomo-gamma-linolenic and 5,8,11,14,17-eicosapentaenoic acids in the sn-2 position of phosphatidylinositol may be explained by their limited availability.

Arachidonic acid metabolites in saliva of patients with squamous cell carcinoma of the head and neck

Alterations in the production of arachidonic acid metabolites by squamous epithelium of the upper aerodigestive tract may play a role in the pathogenesis of squamous cell carcinoma of the head and neck. The levels of cyclooxygenase and lipoxygenase metabolites of arachidonic acid metabolism were measured by radioimmunoassay in the saliva of 51 patients with squamous cell carcinoma of the head and neck and compared with a control group of 27 patients with no history of cancer. Levels of leukotriene B4 were significantly increased in cancer patients (p = 0.02), whereas there were no significant differences in levels of prostaglandin E2 or 15-hydroxy-eicosatetranoic acid. Levels of metabolites did not correlate with a history of tobacco use and did not change in a consistent manner after surgery. The significance of arachidonic acid metabolites in the saliva of patients with squamous cell carcinoma of the head and neck is unknown.

Prostaglandin E2 production in submandibular salivary glands of rats in essential fatty acid deficiency

Three groups of rats were fed an essential fatty acid (EFA)-deficient diet (EFAD), marginally EFA-deficient diet (MEFAD) or a control diet. Arachidonic acid levels in total phospholipids and the ex-vivo production of prostaglandin E2 (PGE2) in the presence of calcium ionophore were measured at 5 and 9 weeks in the submandibular salivary glands (SMSG). The arachidonic acid levels were significantly different among the 3 groups of rats fed the respective diets for 9 weeks. Ex-vivo PGE2 production was significantly decreased in the EFAD group but not in the MEFAD group as compared to the control group. The changes in fatty acid composition, arachidonic acid levels and ex-vivo production of PGE2 were reversed after 5 weeks of feeding the control diet to the EFAD or the MEFAD rats. Since arachidonic acid and PGE2 are involved in signal transduction pathways in the SMSG, an EFA deficiency is likely to modify these pathways.

Effects of benzo(a)pyrene and nicotine on prostaglandin synthesis in buccal pouch and submandibular glands of the Syrian hamster

Adult male Syrian hamsters were treated by swabbing the apex of the buccal pouch with corn oil (control, C), 1 mM benzo(a)pyrene (BP), nicotine (NC), or BP+NC in corn oil, twice daily, 5 days a week. After a 4-week treatment, the pouches and submandibular glands were dissected and used for the determination of endogenous prostaglandin (PG) production and studies on in vitro PG synthesis. Of the three PGs analysed (PGE2, PGF2 alpha and 6-keto-PGF1 alpha), PGE2 was predominant in the pouch and the glands. BP or NC alone had only a weak effect on PG synthesis in both tissues. However, the combination of BP and NC had a synergistic effect, causing diminished PG synthesis in both tissues. In buccal pouch, BP+NC significantly decreased the concentrations of endogenous PGE2 and PGF2 alpha (PGE2: 0.669 +/- 0.254 versus 1.698 +/- 0.460, PGF2 alpha: 0.273 +/- 0.090 versus 0.625 +/- 0.272 ng/g tissue; BP+NC versus C; mean +/- SD, n = 5, p < 0.05). Similarly significant results were also found for in vitro PG synthesis (PGE2: 0.541 +/- 0.249 versus 1.399 +/- 0.340, PGF2 alpha: 1.045 +/- 0.428 versus 2.133 +/- 0.510 ng/g tissue; BP+NC versus C; mean +/- SD, n = 5, p < 0.05). In submandibular glands, BP+NC significantly diminished the concentration of endogenous PGE2 (1.183 +/- 0.175 versus 2.379 +/- 0.488 ng/g tissue; BP+NC versus C; mean +/- SD, n = 5, p < 0.05). The synthesis of 6-keto-PGF1 alpha in both tissues, and the synthesis of PGF2 alpha in submandibular gland, were slightly decreased with all treatments.

Expression of prostaglandin E2 receptor in hamster buccal pouch: effect of benzo (a) pyrene and nicotine

Prostaglandin E2 (PGE2) plays an important role in the maintenance of oral mucosal integrity. In this study, we characterized PGE2 receptor binding in the buccal mucosa of Syrian hamster and assessed the effect of nicotine (NC) and benzo (a) pyrene (BP), the two major ingredients in cigarette smoke, on this receptor. Adult male animals were treated for 4 weeks by apical swabbing of the buccal pouch with corn oil (control, C), 1 mM NC, BP, or NC + BP in corn oil, twice a day, 5 days a week. The results obtained with the untreated group revealed the presence of a specific PGE2 receptor consisting of two binding sites (high affinity with Kd = 1.52 nM and Bmax = 37 fmol/mg protein and low affinity with Kd = 813 nM and Bmax = 1.29 pmol/mg protein). The treatment with NC, BP, and NC + BP caused a significant decrease in PGE2 receptor binding (specific binding: 10.20 +/- 0.42, 6.84 +/- 1.32**, 6.58 +/- 0.67** and 5.88 +/- 1.03** fmol/mg protein; C, NC, BP, and NC+BP, respectively; Mean +/- SD, n = 5, **p < 0.01). The data suggest that decreased receptor binding for PGE2 in the buccal mucosa may be the cause for the adverse effect of cigarette smoke on the health of oral mucosa.

Cigarette smoking reduces human salivary eicosanoids

The effect of cigarette smoking on salivary eicosanoid levels was investigated in 10 smoker and 10 non-smoker volunteers. The smokers consumed an average of 20 cigarettes/day for the past 5 years or longer. The smoking status was validated by salivary cotinine level. Eicosanoids were extracted from saliva with ethanol, and the radioimmunoassay was performed to determine the concentrations of four major eicosanoids, i.e. prostaglandin E2 (PGE2), PGF2 alpha, 6-sulphidopeptide-containing leukotrienes (LTs) and 12-hydroxyeicosatetraenoic acid (12-HETE). The levels of PGE2, PGF2 alpha, and LTs were significantly lower in the saliva of smokers as compared to that of the non-smokers (1.74 +/- 0.32 vs 2.41 +/- 0.64, p = 0.006; 0.36 +/- 0.12 vs 0.54 +/- 0.18, p = 0.04; 2.24 +/- 0.96 vs 4.92 +/- 1.29, p = 0.006; mean +/- SD, ng/ml saliva). No significant differences were found in the levels of 12-HETE between the two groups. The results suggest that cigarette smoking reduces the concentrations of both the cyclooxygenase and 5-lipoxygenase products in saliva.

Arachidonic acid, prostaglandin E2 and leukotriene C4 levels in gingiva and submandibular salivary glands of rats fed diets containing n-3 fatty acids

The effect of dietary n-3 fatty acids on prostaglandin E2 (PGE2) and leukotriene C4 (LTC4) levels in rat salivary glands and gingiva was examined in two separate nutritional studies. In the first set of experiments, two groups of male weanling Sprague-Dawley rats were fed semipurified diets containing 10% corn oil (control group) or 10% menhaden oil (experimental group). Rats were killed after 8 wk on the diets; the fatty acid composition of total phospholipids and the concentrations of PGE2 and its precursor, arachidonic acid, were measured in gingiva and submandibular salivary glands (SMSG). Dietary n-3 fatty acids were incorporated into the tissue phospholipids. Arachidonic acid levels were reduced by 56% in gingiva and SMSG of rats fed menhaden oil compared with the control rats fed the diet containing corn oil. The concentrations of PGE2 in SMSG and gingiva of rats fed the diet containing menhaden oil were reduced by 74% and 83%, respectively. In a subsequent nutritional study, we tested whether the diet-induced reduction in tissue arachidonic acid levels would also result in a corresponding decrease in LTC4 production. Three groups of rats were fed diets containing 5% corn oil (group 1), 4% ethyl ester concentrate of n-3 fatty acids plus 1% corn oil (group 2), or 5% ethyl ester concentrate of n-3 fatty acids (group 3). After 6 wk of feeding, gingiva and SMSG were analyzed for arachidonic acid content and in vitro production of LTC4.(ABSTRACT TRUNCATED AT 250 WORDS)

Impairment by ethanol of prostaglandin production in rat salivary glands

Sublingual salivary acini and submandibular tissue were incubated in DMEM medium in the presence of various concentrations (0-5%) of ethanol and the content of the three major prostaglandins, PGE2, PGF2 alpha and 6-keto-PGF1 alpha, were determined by radioimmunoassay. In In the sublingual gland, ethanol caused a decrease in PGE2 and PGF2 alpha levels, but had no effect on 6-keto-PGF1 alpha, while all three prostaglandins were affected in the submandibular gland. At 2.5% ethanol, the production of PGF2 alpha and PGE2 in sublingual gland decreased by 10% and reached maximum inhibition at 5% ethanol, at which concentration there was a 20 and 30% decrease in their levels. In submandibular gland, 2.5% ethanol caused a 20% decrease in PGE2, 30% in PGF2 alpha and 50% in 6-keto-PGF1 alpha; 40% inhibition in PGE2, 57% in 6-keto-PGF1 alpha and 65% in PGF2 alpha occurred in the presence of 5% ethanol. These findings suggest that alcohol impairs the function of salivary glands by inhibiting prostaglandin production.

Prostaglandin E2 receptor of rat submandibular salivary glands

The binding characteristics of the PGE2 receptor were investigated in membrane preparations from these glands. Specific [3H]PGE2 binding was linear as a function of the membrane protein concentration and reached steady state by 40 min of incubation at 37 degrees C under neutral pH. Scatchard analysis of the binding data produced a curvilinear plot with a Kd of 0.18 nM and Bmax of 1.02 fmol/mg protein for the high-affinity binding sites, and a Kd of 181 nM and Bmax of 5.72 pmol/mg protein for the low-affinity binding sites. A competitive displacement study indicated that the receptor was specific for prostaglandins of the E series. The study is the first to demonstrate the presence of the PGE2 receptor in rat submandibular gland and to provide its biochemical features.