Temporal Reduction in Size of Salivary Acinus in Rats Induced by Theophylline

Repeated administration of theophylline, a phosphodiesterase inhibitor, induces the enlargement of the salivary glands in rats. Time-course changes after a single administration of theophylline were examined in the salivary glands, including phosphodiesterase enzyme activity, and the expression of aquaporin 5 (AQP5), a water channel. We also examined the contribution of β-adrenergic receptors to theophylline-induced salivary changes. Male F344 rats were given 50 mg/kg of theophylline intraperitoneally either alone or concurrently with a 10 mg/kg subcutaneous injection of propranolol. After treatment with theophylline alone, the weight and histology of the submaxillary and parotid glands were examined. Phosphodiesterase activity and AQP5 were detected by enzyme- and immuno-histochemistry, respectively. At 4 hours, 8 hours, or both, organ weights were decreased with depletion of secretory vesicles in the acinar cells. In the submaxillary glands, reduced activity of phosphodiesterase and increased expression of AQP5 in the intercalated ducts were observed at 4 hours. When co-administered, propranolol partially abolished theophylline-induced glandular reduction. These results suggest that the theophylline-induced transient reduction in size of the salivary glands is attributable not only to phosphodiesterase inhibition but also to β-adrenergic receptor activation and that the intercalated ducts in submaxillary glands play a role in the production of saliva.

Role of GAD peptides p217 and p290 in the repair of INS receptor in salivary tissues of type 1 diabetic mice

Glutamate decarboxylase or glutamic acid decarboxylase (GAD) is a protein associated with autoimmune diseases, including type-1 diabetes. This disease is primarily associated with the occurrence of a specific isoform: GAD65. Conversely, some specific peptides of this protein may block autoimmunity in diabetes. In this respect, understanding the relationship between GAD and the development of diabetes is important, and it is necessary to understand the role of each GAD peptide to design effective autoimmune diabetes treatments. The purpose of the present study was to analyze the effects of treatment with GAD-derived peptides p217 and p290 on INS receptors in the salivary epithelium of nonobese diabetic (NOD) animals. Three groups of 7 mice each were studied: I, BALB/c mice (control); II, NOD mice; and III, NOD mice treated with peptides p290 and p217. Groups I and II only received buffered saline solution. Glucose levels were measured daily during the 21 days of the experiment. After the study, the animals were euthanized and the parotid and submandibular glands were removed for the analysis of INS-R by fluorescence microscopy. Therapy with two peptides together was associated with reduced glucose levels in NOD mice and intense INS-R expression in both salivary organs. Our approach of combining GAD p217 and p290 peptides contributed to hormonal balance and promoted the repair of INS-R.

BAEE esterase (kallikrein-like) activity in parotid saliva of normal rats and rats with various forms of experimental hypertension (genuine, renovascular and DOCA salt hypertension)

A technique for continuous and quantitative collection of parotid saliva including salivary flow rate determination for in vitro experiments in rats is described. Kallikrein-like activity in parotid saliva of rats with various forms of arterial hypertension (genuine, renovascular and DOCA salt hypertension) was studied. Kallikrein-like excretion was measured by its estoerolytic activity using benzoyl arginine ethyl ester (BAEE) as a substrate. The levels of kallikrein-like activity in parotid saliva of normotensive control rats ranged between 2.5 and 4.0 mU/min during salivary flow stimulation with pilocarpine. In all forms of experimental hypertension kallikrein-like activity in saliva was increased two-to fourfold. This increase was not related to the activity of the renin-angiotensin system.

Effects of isoproterenol on aquaporin 5 levels in the parotid gland of mice in vivo

In the membrane fraction of mouse parotid gland (PG), the protein level of aquaporin 5 (AQP5), a member of the water channel family, was increased by injection (ip) of isoproterenol (IPR), a β-adrenergic agonist, at 1 h, and stayed at high levels until 6 h; this change occurred simultaneously as amylase secretion. The AQP5 level then decreased and returned toward the original level at 12-48 h. After IPR injection, the AQP5 mRNA gradually increased and reached a maximum at 24 h. The facts suggest a rapid appearance of AQP5 at plasma membrane by IPR and subsequent degradation/metabolism by activation of proteolytic systems. Pretreatment of animals with two calpain inhibitors, N-Ac-Leu-Leu-methininal (ALLM) and calpeptin, as well as a protein synthesis inhibitor, cycloheximide (CHX), significantly suppressed the IPR-induced AQP5 degradation in the PG membrane fraction; such suppression was not observed by two proteasome inhibitors, MG132 and lactacystin, or the lysosome denaturant chloroquine, although most of these inhibitors increased AQP5 protein levels in unstimulated mice. The AQP5 protein was also degraded by μ-calpain in vitro. Furthermore, we demonstrated that μ-calpain was colocalized with AQP5 in the acinar cells by immunohistochemistry, and its activity in the PG was increased at 6 h after IPR injection. These results suggest that the calpain system was responsible for IPR-induced AQP5 degradation in the parotid gland and that such a system was coupled to the secretory-restoration cycle of amylase in the PG.

Immunogold labeling of carbonic anhydrase isozyme (CA-VI) in secretory granules of human parotid glands

Serous granules in the human parotid gland have a well-defined substructure, consisting of a dense spherule suspended in a moderately dense matrix. Immunogold labeling with an antibody against carbonic anhydrase VI revealed that this enzyme is localized within the matrix and is absent from the spherule. This location matches that of a number of other salivary gland proteins. Cell organelles involved in the secretory pathway are devoid of label. Labeling was not observed in any ductular component of the gland.

[Effect of sijunzi decoction on salivary amylase secretion disorder and VIP-cAMP signaling pathway in splenasthenic rats]

OBJECTIVE

To observe the effect of Sijunzi Decoction on secretion disorder of salivary amylase in splenasthenic rat and its mechanism.

METHODS

The model group rats received reserpine 0.5 mg/kg through subcutaneous injection while the control group rats received the same volume of saline for 8 days. After being modeled, the model group were divided into treatment group and model control group, treatment group were given orally Sijunzi Decoction, model control group and normal group were fed the same amount of distilled water for 4 weeks. The animal were anaesthetized and the left parotid was removed, the wounds were sutured. When the animals were awake but drowsy, 20 microL 10% glacial acetic acid was applied on the apex of the tongue once a minute for 30 minutes, removed the right parotid gland of the animals. The samples were frozen and amylase activity and VIP, cyclic adenosine monophosphate (cAMP) content and VAMP-8, SNAP-23 protein expression in the parotid glands were detected.

RESULTS

Change of sAA in parotid acinar was not significantly different between treatment group and normal groups, but higher in model control groups after acid stimulation. The VIP and PKA contents were not significantly different among three groups. VIP, cAMP content and PKA activity increased significantly in normal group while VIP increased slightly, cAMP and PKA activity decreased in model control groups, which returned to some degrees in treatment group after acid stimulation. Expression of VAMP-8 protein was not significantly different between treatment group and model control groups, while expression of SNAP-23 was lower in model control groups, expression of VAMP-8 and SNAP-23 was higher in treatment group than which in model control groups.

CONCLUSION

Sijunzi Decoction has a certain effect on secretion disorder of salivary amylase in splenasthenic rat, which mechanism may be related to recover changes of VIP-cAMP signal pathway in the splenasthenic rat's parotid gland cells,including increase VIP content and expression of VAMP-8 and SNAP-23.

Effect of irradiation on microvascular endothelial cells of parotid glands in the miniature pig

PURPOSE

To evaluate the effect of irradiation on microvascular endothelial cells in miniature pig parotid glands.

METHODS AND MATERIALS

A single 25-Gy dose of irradiation (IR) was delivered to parotid glands of 6 miniature pigs. Three other animals served as non-IR controls. Local blood flow rate in glands was measured pre- and post-IR with an ultrasonic Doppler analyzer. Samples of parotid gland tissue were taken at 4 h, 24 h, 1 week, and 2 weeks after IR for microvascular density (MVD) analysis and sphingomyelinase (SMase) assay. Histopathology and immunohistochemical staining (anti-CD31 and anti-AQP1) were used to assess morphological changes. MVD was determined by calculating the number of CD31- or AQP1-stained cells per field. A terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) apoptosis assay was used to detect apoptotic cells. The activity of acid and neutral Mg(2+)-dependent SMase (ASMase and NSMase, respectively) was also assayed.

RESULTS

Local parotid gland blood flow rate decreased rapidly at 4 h post-IR and remained below control levels throughout the 14-day observation period. Parotid MVD also declined from 4 to 24 hours and remained below control levels thereafter. The activity levels of ASMase and NSMase in parotid glands increased rapidly from 4 to 24 h post-IR and then declined gradually. The frequency of detecting apoptotic nuclei in the glands followed similar kinetics.

CONCLUSIONS

Single-dose IR led to a significant reduction of MVD and local blood flow rate, indicating marked damage to microvascular endothelial cells in miniature pig parotid glands. The significant and rapid increases of ASMase and NSMase activity levels may be important in this IR-induced damage.

Sodium tungstate on some biochemical parameters of the parotid salivary gland of streptozotocin-induced diabetic rats: a short-term study

Several studies have shown the antidiabetic properties of sodium tungstate. In this study, we evaluated some biochemical parameters of the parotid salivary gland of streptozotocin-induced diabetic rats treated with sodium tungstate solution (2 mg/ml). The studied groups were: untreated control (UC), treated control (TC), untreated diabetic (UD), and treated diabetic (TD). After 2 and 6 weeks of treatment, parotid gland was removed and total protein and sialic acid (free and total) concentration and amylase and peroxidase activities were determined. Data were compared by variance analysis and Tukey test (p < 0.05). The sodium tungstate treatment modestly decreased the glycemia of streptozotocin-induced diabetic rats. At week 2 of the study, parotid gland of diabetic rats presented a reduction of total protein concentration (55%) and an increase of amylase (120%) and peroxidase (160%) activities, free (150%) and total (170%) sialic acid concentration. No alteration in the evaluated parameters at week 6 of the study was observed. Sodium tungstate presented no significant effect in parotid gland. Our results suggest that diabetes causes initial modification in biochemical composition of parotid. However, this gland showed a recovery capacity after 6 week of the experimental time. Sodium tungstate has no effect in peripheral tissues, such as salivary glands.

Susceptibility of mammalian deoxyribonucleases I (DNases I) to proteolysis by proteases and its relationships to tissue distribution: Biochemical and molecular analysis of equine DNase I

Equine (Equus caballus) deoxyribonuclease I (DNase I) was purified from the parotid gland, and its 1295-bp cDNA was cloned. The mature equine DNase I protein consisted of 260 amino acid residues. The enzymatic properties and structural aspects of the equine enzyme were closely similar to those of other mammalian DNases I. Mammalian DNases I are classified into three types--pancreatic, parotid and pancreatic-parotid-based on their tissue distribution; as equine DNase I showed the highest activity in the parotid gland, it was confirmed to be of the parotid-type. Comparison of the susceptibility of mammalian DNases I to proteolysis by proteases demonstrated a marked correlation between tissue distribution and sensitivity/resistance to proteolysis; pancreatic-type DNase I shared properties of resistance to proteolysis by trypsin and chymotrypsin, whereas parotid-type DNase I did not. In contrast, pancreatic-parotid-type DNase I exhibited resistance to proteolysis by pepsin, whereas the other enzyme types did not. However, site-directed mutagenesis analysis revealed that only a single amino acid substitution could not account for acquisition of proteolysis resistance in the mammalian DNase I family during the course of molecular evolution. These properties are compatible with adaptation of mammalian DNases I for maintaining their activity in vivo.

Evidence for amylase release by cGMP via cAMP-dependent protein kinase in rat parotid acinar cells

Amylase release from the rat parotid gland is primarily mediated by a cAMP-dependent protein kinase (PKA). We previously reported that cGMP/cGMP-dependent protein kinase (PKG) signaling evokes amylase release. In the present study, we investigated whether cGMP-mediated amylase release might be due to cGMP/PKA signaling, as well as cGMP/PKG pathway. Activation of PKA by cGMP was required 100-1000-fold greater concentration than activation by cAMP in a parotid cytosol fraction. Synergistic activation of PKA by the combination of physiological cAMP and low concentration of cGMP was observed. Amylase release from intact acinar cells was synergistically stimulated by the combination of diBu-cAMP and 8-pCPT-cGMP. cGMP dose-dependently stimulated amylase release from saponin-permeabilized parotid acinar cells. Phosphorylation by cGMP produced phosphorylated proteins of the same size as those produced by cAMP. Phosphorylation by cGMP was inhibited by the addition of PKA inhibitor, H-89. These results suggest that cGMP activates both PKG and PKA. Thus, it appears that both cGMP/PKG and cGMP/PKA pathways mediate amylase release from rat parotid acinar cells.

Isoproterenol increases sorting of parotid gland cargo proteins to the basolateral pathway

Exocrine cells have an essential function of sorting secreted proteins into the correct secretory pathway. A clear understanding of sorting in salivary glands would contribute to the correct targeting of therapeutic transgenes. The present work investigated whether there is a change in the relative proportions of basic proline-rich protein (PRP) and acidic PRPs in secretory granules in response to chronic isoproterenol treatment, and whether this alters the sorting of endogenous cargo proteins. Immunoblot analysis of secretory granules from rat parotids found a large increase of basic PRP over acidic PRPs in response to chronic isoproterenol treatment. Pulse chase experiments demonstrated that isoproterenol also decreased regulated secretion of newly synthesized secretory proteins, including PRPs, amylase and parotid secretory protein. This decreased efficiency of the apical regulated pathway may be mediated by alkalization of the secretory granules since it was reversed by treatment with mild acid. We also investigated changes in secretion through the basolateral (endocrine) pathways. A significant increase in parotid secretory protein and salivary amylase was detected in sera of isoproterenol-treated animals, suggesting increased routing of the regulated secretory proteins to the basolateral pathway. These studies demonstrate that shifts of endogenous proteins can modulate regulated secretion and sorting of cargo proteins.

Molecular alterations of parotid saliva in infantile chronic recurrent parotitis

Infantile chronic recurrent parotitis (ICRP) is an insidious disease whose etiopathogenesis remains an enigma. Alterations in the physical appearance of parotid saliva from ICRP patients have been frequently reported. However, sialochemical studies in regard to ICRP are very rare. The aim of this study was to determine whether saliva of ICRP patients presents major physicochemical and biochemical alterations compared with saliva from paired healthy controls. Parotid, whole, and submandibular/sublingual saliva was collected at an asymptomatic stage from 33 ICRP patients (5-16 y old, both sexes) and from 33 sex- and age-matched healthy controls. Saliva was analyzed for protein concentration, mode of protein diffusion on cellulose membranes, unidimensional sodium dodecylsulfate (SDS)-polyacrylamide gel electrophoresis protein profiles and zymographic profiles of metalloproteinase 2 (MMP-2) and metalloproteinase 9 (MMP-9). Parotid saliva of ICRP patients showed an increased protein concentration, altered mode of protein diffusion, a higher frequency of polypeptide bands of 43, 37, 33, 29, 26, 16, and 10 kD, higher asymmetry in the polypeptide profiles of both contralateral parotid saliva, and an increase in the frequency of MMP-2 and MMP-9. Parotid saliva of patients with ICRP is molecularly altered with respect to normal saliva. Some of the molecular differences could be related to the etiopathogenesis of the disease.

Ca(2+)/calmodulin-dependent cyclic nucleotide phosphodiesterase in cGMP metabolism in rabbit parotid acinar cells

Muscarinic cholinergic receptor activation provokes cGMP formation in parotid acinar cells. We investigated the involvement of Ca(2+)/calmodulin-dependent cyclic nucleotide phosphodiesterase (PDE1) in cGMP breakdown in rabbit parotid acinar cells. The muscarinic agonist carbachol stimulated cGMP formation in the cells. The carbachol-induced cGMP formation was enhanced in the presence of 8-methoxymethyl-3-isobutyl-1-methylxanthine (MM-IBMX), a PDE1 inhibitor. cGMPPDE activity in rabbit parotid acinar cells was reduced by about 25% in the absence of Ca(2+)/ calmodulin or in the presence of MM-IBMX. Ca(2+)/calmodulin-dependent cGMP-PDE in rabbit parotid acinar cells was purified using Calmodulin-Sepharose 4B and Mono Q ion-exchange column chromatography. Two dominant fractions with cGMP-PDE activity, referred to as the P-1 and P-2 fractions, were eluted from the Mono Q ion-exchange column. The Km values for cGMP of PDE in the P-1 and P-2 fractions were 0.82 microM and 0.40 microM, respectively, which were much lower than that for cAMP. The EC(50) for Ca(2+) and calmodulin of PDEs in the P-1 and P-2 fractions were 458 nM and 426 nM, respectively, and 32 nM and 137 nM, respectively. Protein bands that crossreacted with anti-PDE1A antibody were detected. These results suggest that Ca(2+)/calmodulin-dependent PDE, PDE1A, is involved in cGMP breakdown in rabbit parotid acinar cells.

Immunohistochemical investigations of the influence of botulinum toxin A on the immunoreactivity of nNOS in the parotid gland of the rat

PURPOSE

We wanted to prove the hypothesis that local injections of botulinum toxin A have an influence on the immunoreactivity of neuronal nitric oxide synthase (nNOS) in parotid glands of adult rats.

MATERIALS AND METHODS

Our group carried out immunohistochemical reaction of neuronal nitric oxide synthase (nNOS) in the parotid gland of female adult Wistar rats, in native (untreated) glands and after intraglandular injection of botulinum toxin A under general anesthesia. The immunoreactivity of nNOS was investigated on different times after injection.

RESULTS

Compared with the untreated glands, there was a significant decrease of nNOS in the treated organs that became stronger with extended toxin exposure time. After our laboratory in a pilot study had already shown in general a decrease of nNOS immunoreactivity after injection of botulinum toxin A into the cephalic salivary glands of the rat, the present study shows more explicit data on the effect of botulinum toxin A injection on a higher number of examined parotid glands and analyzes a time course of the effect duration.

CONCLUSIONS

In our study, it was shown that botulinum toxin A had an influence on the immunoreactivity of neuronal nitric oxide synthase (nNOS) in parotid glands. Participation of nitric oxide (NO) in the regulation of secretion from the parotid gland of the rat seems to be likely. It might be assumed that the influence of botulinum toxin A on nNOS in the parotid gland of the rat is able to explain the sometimes longer duration of toxin effect at the neuroglandular junction than at the motor endplate.

Activity, distribution and regulation of phosphofructokinase in salivary gland of rats with streptozotocin-induced diabetes

Although the influence of diabetes on salivary glands is well studied, it still presents conflicting results. In this work, the regulation of the phosphofructokinase-1 enzyme (PFK-1) was studied utilizing the salivary glands of rats. Diabetes was induced by a single intraperitoneal injection of streptozotocin (60 mg/Kg of body weight) in rats (180-200 g). The animals were killed 30 days after the induction of diabetes and the submandibular and parotid salivary glands were used. Hyperglycemia was evaluated by blood sugar determination. The distribution of PFK-1 between the soluble and cytoskeleton fractions, the phosphate content of PFK-1, the content of fructose-2,6-bisphosphate and the activity of the PFK-2 enzyme were determined. The calculated relative glandular weight showed a higher value for the parotid gland in comparison with the control, but not for the submandibular gland. The activity of PFK-1 expressed per gland showed no variation between diabetic and control animals. However, considering the specific activity, the soluble enzyme presented a value 50% higher than that of the control and the cytoskeleton bound form increased by 84% compared to the control. For the parotid gland, no difference in the specific activity between diabetic and control animals was observed. On the other hand, the activity per gland of the soluble enzyme increased in the diabetic animals. The phosphate content of PFK-1 increased in the submandibular and parotid glands of diabetic rats. Both the content of fructose-2,6-bisphosphate and the active form of PFK-2 were reduced in the diabetic glands. In conclusion, the increase in the activity of PFK-1 observed in the salivary glands of rats with streptozotocin-induced diabetes does not seem to be due to its modulator fructose-2,6-bisphosphate.

Constitutive (HO-2) and inducible (HO-1) haem oxygenase in pleomorphic adenomas of the human parotid: an immunocytochemical study

This study examines the expression HO-1 and HO-2 isozymes in human parotid pleomorphic adenomas. They are members of the heat shock protein family, and are thought to play a role in the regulation of tumoral blood flow. Immunocytochemistry using antibodies specific for HO-1 and HO-2 were undertaken in 12 pleomorphic adenoma specimens, all sections of which contained adjacent normal salivary tissue. Normal salivary gland acini and ducts displayed significantly stronger immunoreactivity for HO-2 compared to tumour cells (p < 0.001). Expression for HO-1 was minimal in both normal salivary gland acini and tumour cells with no difference (p = 1.000). However, positive staining for HO-1 was seen in normal salivary ducts and in pleomorphic adenomas showing ductal differentiation. In conclusion, this is the first study to examine the expression of HO-1 and HO-2 within normal salivary glands and pleomorphic adenomas. Our findings suggest that HO may be implicated in the pathogenesis of salivary pleomorphic adenomas.

Cyclooxygenase-2 expression in Warthin's tumour

Objectives: To determine whether cyclooxygenase-2 (COX-2) is overexpressed in Warthin's tumours, and to characterize its pattern of expression.

Methods: Twenty-one paraffin-embedded Warthin's tumour specimens were analysed by immunohistochemical staining for expression of human COX-2. Semi-quantitative analysis of the staining was performed.

Results: In all of the specimens, we found that there was overexpression of COX-2 within the epithelial component of the tumours, with no expression in the lymphoid components. There was also overexpression of COX-2 in the salivary duct system of normal parotid tissue.

Conclusions: Our results suggest that COX-2 is up-regulated in the epithelial component of Warthin's tumours. Our findings support the hypothesis that Warthin's tumours originate from heterotopic ductal epithelial cells of the parotid gland. The role of COX-2 expression in the pathogenesis of Warthin's tumours remains to be determined.

Fructokinase activity in rat liver, ileum, parotid gland, pancreas, pancreatic islet, B and non-B islet cell homogenates

The presence of fructokinase (ketohexokinase) in rat pancreatic islet homogenates was previously documented. However, no information was so far available on the activity of this enzyme in islets relative to that in other tissues and on the respective contribution of insulin-producing B cells and non-B islet cells. The present study provides such an information. The activity of fructokinase, as assessed by the phosphorylation of 1.0 mM D-fructose, was compared to that of hexokinase isoenzyme(s), as measured in the presence of 1.0 mM D-glucose, and further characterized by its heat-resistance, K+ dependency and resistance to the inhibitory action of D-mannoheptulose. As judged from the results obtained in heated homogenates, the activity of fructokinase, expressed relative to protein content (nmol/min per mg protein) was highest in liver (21.5 +/- 2.5; n = 11) and lowest in parotid gland (0.16 +/- 0.09; n = 3), with in-between values in ileum (2.45 +/- 0.53; n = 3), pancreas (0.82 +/- 0.11; n = 11) and pancreatic islets (0.46 +/- 0.07; n = 6). The paired ratio between fructokinase and hexokinase isoenzyme activity was also highest in liver (548 +/- 45%; n = 8) and lowest in parotid gland (0.93 +/- 0.52%; n = 3). Such a ratio was not significantly different in pancreas, islets and purified B or non-B islet cells, with an overall mean value of 2.57 +/- 0.46% (n = 12). The present findings thus unambiguously document the presence of fructokinase activity in all cell types under consideration, except possibly parotid cells, with the following hierarchy: liver > ileum > pancreas. Relative to paired hexokinase activity, no obvious difference was found for fructokinase activity in B versus non-B islet cells.

The role of estrogen and Cu, Zn-SOD on histological changes after menopause in female rat parotid

OBJECTIVE

Generally, postclimacteric women are susceptible to xerostomia. Therefore, correlations between xerostomia and sex hormones have been studied. Previously, we reported that a reduction of estrogen (belongs to female hormones) could have influence on age-related histological changes in female rat parotids induced by apoptosis. One component of inducing apoptosis is free radical. Recently, it have been noticed that free radical have an effect on aging. A living body has superoxide dismutase (SOD), which can eliminate free radical. SOD decreases according as aging. Therefore, we investigated that the role of estrogen and Cu, Zn-SOD on histological changes after menopause in female rat parotid.

METHODS

Apoptosis was observed by TUNEL staining. Cu, Zn-SOD was examined by immunochemical staining. Cu, Zn-SOD and apoptosis of rats having undergone only ovariectomy were compared to rats with natural aging and to those having been administered estrogen infusion after ovariectomy.

RESULTS

In natural aging groups, TLI (TUNEL labeling index) mean of postmenopausal rats significantly showed higher than premenopause. On groups of ovariectomized rat, TLI means with estrogen infusion after ovariectomy were significantly lower than only ovariectomy. The positive Cu, Zn-SOD in groups with estrogen infusion after ovariectomy were stronger than a group with only ovariectomy.

CONCLUSIONS

Our results suggested that estrogen and Cu, Zn-SOD could suppress histologically aging changes in parotid of female rat induced by apoptosis and that estrogen could have influence on the production of Cu, Zn-SOD.

One-step purification of mammalian deoxyribonucleases I and differences among pancreas, parotid, and pancreas-parotid (mixed) types based on species-and organ-specific N-linked glycosylation

Mammalian deoxyribonucleases I (DNase I) are classified into three types, namely, pancreas, parotid, and pancreas-parotid (mixed), based on differences in their tissue concentrations. In this study, DNase I purification by concanavalin A-wheat germ agglutinin mixture-agarose column from rat (parotid type), rabbit (mixed type), and pig (pancreas type) is described. This method permits a relatively easy one-step purification of DNase I from rat and rabbit parotid glands, the rat submaxillary gland, and porcine pancreas. To elucidate differences among the three types, these DNases I were subjected to enzymatic deglycosylation either by peptide N-glycosidase F (PNGase F) or endoglycosidase H (Endo H). Following deglycosylation, digests were separated on DNA-casting polyacrylamide gel electrophoresis. PNGase F produced a single lower mobility product in all samples. Endo H produced a double band in rat and rabbit parotid glands and porcine pancreas, and a single band in the rabbit pancreas corresponding with the PNGase F product. DNase I activity of the porcine pancreas was completely extinguished by deglycosylation, while that of the parotid glands and rabbit pancreas was unaffected. Our results suggest that the distinct properties of DNase I exhibited by the three types may be attributed to differences in the extent of post-translational N-linked glycosylation of the enzyme.

Endogenous signalling system involved in parotid gland adenosine A(1) receptor-amylase release

AIM

In this study, we have determined signalling pathways involved in adenosine A(1) receptor (A(1) receptor)-dependent stimulation of amylase release in rat parotid gland.

METHODS

Amylase release, binding and cyclic adenosine monophosphate (cAMP) assays, inositol phosphates (IPs) production and nitric oxide synthase (NOS) activity in the presence of cyclopentyl-1,3-dipropylxanthine (CPA) alone or in the presence of different inhibitory drugs were performed.

RESULTS

The binding parameters of specific A(1) antagonist [(3)H]-cyclopentyl 1,3-dipropilxanthine ([(3)H]-DPCPX) in parotid gland membranes show a population of high affinity sites with K(d) (nm) 0.53 +/- 0.06 and B(max) (fmol mg(-1) protein) 122.6 +/- 10.2. CPA stimulation of A(1) receptor exerts an increase in amylase release, IPs accumulation, cAMP production and NOS activity. All these A(1) agonist effects were blocked by the A(1) receptor antagonist DPCPX. Inhibitors of phospholipase C (PLC), calcium/calmodulin (CaM), protein kinase C (PKC), and adenylate cyclase, but not NOS, activities attenuated the CPA stimulatory effect on amylase release. The effect of CPA on amylase release significantly correlated with its action either on cAMP or on IPs accumulation.

CONCLUSION

These results suggest that CPA activation of parotid gland A(1) receptor induces a stimulatory effect on amylase release associated with increased production of cAMP and IPs accumulation. The mechanism appears to occur secondarily to stimulation of phosphoinositide turnover via PLC activation. This, in turn, triggers cascade reactions involving CaM and PKC. The CPA stimulation of NOS does not appear to participate in amylase release.

Identification and characterization of tyrosylprotein sulfotransferase from human saliva

Tyrosylprotein sulfotransferase (TPST), the enzyme responsible for the sulfation of tyrosine residues, has been identified and characterized in submandibular salivary glands previously (William et al. Arch Biochem Biophys 338: 90-96). Tyrosylprotein sulfotransferase catalyses the sulfation of a variety of secretory and membrane proteins and is believed to be present only in the cell. In the present study, this enzyme was identified for the first time in human saliva. Analysis of human saliva and parotid saliva for the presence of tyrosylprotein sulfotransferase revealed tyrosine sulfating activity displayed by both whole saliva and parotid saliva at pH optimum of 6.8. In contrast to tyrosylprotein sulfotransferase isolated from submandibular salivary glands, salivary enzyme does not require the presence of Triton X-100, NaF and 5'AMP for maximal activity. Similar to the submandibular TPST, the enzyme from saliva also required MnCl₂ for its activity. Maximum TPST activity was observed at 20mM MnCl₂. The enzyme from saliva was immunoprecipitated and purified by immunoaffinity column using anti-TPST antibody. Affinity purified salivary TPST showed a single band of 50-54 kDa. This study is the first report characterizing a tyrosylprotein sulfotransferase in a secretory fluid.

Lack of nitric oxide-mediated regulation of amylase secretion stimulated by VIP in parotid glands of NOD mice

The non-obese diabetic (NOD) mouse is chosen among other experimental models to study autoimmune sialadenitis resembling Sjögren's syndrome (SS), because of its unique characteristic of developing salivary dysfunction. Based on the deep loss of nitric oxide synthase (NOS) activity in parotid glands of NOD mice observed from early stages of disease and the inhibitory effect of nitric oxide (NO) donors on amylase secretion in normal salivary glands, our goal was to investigate whether parotid glands from NOD mice lacking NOS activity presented this regulatory mechanism of amylase secretion. We found that parotid glands from NOD mice lack nitric oxide-mediated regulation of amylase secretion in response to VIP stimulation. The lack of regulation might be assigned to the loss of NOS activity as derived from the results with NOS inhibitors and increasing concentrations of VIP. These functional differences observed in NOD vs. BALB/c parotid glands occur in the absence of immune infiltrates in exocrine tissue, and it is not related to cAMP accumulation. NO-mediated regulation of amylase secretion was not observed in BALB/c submandibular glands to the same extent as described in parotid glands and was absent in submandibular glands of NOD mice.

Soluble guanylyl cyclase is localised in the acinar cells and participates in amylase secretion in rat parotid gland

It is well known that the muscarinic cholinergic agonists, carbachol and methacholine, enhance nitric oxide synthase (NOS) activity, and also stimulate salivary secretion. In the present study, we investigated whether salivary secretion by muscarinic cholinergic stimulation is mediated through the NO/cGMP signaling pathway in rat salivary glands. Since NO activates soluble guanylyl cyclase (sGC) and cGMP may function as a mediator, the localisation of sGC was investigated in the salivary glands. sGC was localized in both the acinar and duct cells of the rat parotid and sublingual glands, and localized only in the acinar cells of the submandibular glands. S-Nitroso-glutathione (NO generator; GSNO) and YC-1 (NO-independent sGC activator) stimulated sGC in the cytosol to synthesise cGMP. The combination of GSNO and YC-1 stimulated sGC synergistically. Carbachol, GSNO and YC-1 enhanced amylase release from the rat parotid glands. Amylase release stimulated by carbachol and GSNO was inhibited by addition of the sGC inhibitor, ODQ, and cGMP-dependent protein kinase inhibitor, KT-5823. These results indicate that amylase release may be mediated through the NO/cGMP signaling pathway.

Expression and biological effects of CB1 cannabinoid receptor in rat parotid gland

Experiments were designed to determine whether cannabinoids affect salivary gland function. For this purpose, the effect of anandamide on cAMP accumulation, amylase release and Na+-K+-ATPase activity was studied in rat parotid glands. Anandamide induced a concentration-dependent increase in cAMP and led to amylase release but inhibited Na+-K+-ATPase activity. These effects were blocked by the CB1 cannabinoid receptor antagonist, AM281. The inhibition of adenylyl cyclase activity by SQ 22536 impaired amylase release and Na+-K+-ATPase inhibition. The effect of anandamide on cAMP accumulation significantly correlated with its action either on amylase release or on Na+-K+-ATPase activity. Such correlation strongly supports the view that the effect of anandamide on amylase release and Na+-K+-ATPase activity is the result of cAMP accumulation. The relative potencies of the CB1 cannabinoid receptor antagonist, AM281, to block these three functional responses were similar, supporting the view that anandamide actions in parotid glands were achieved through a single receptor subtype, the CB1. Binding studies using the selective cannabinoid CB1 receptor antagonist, [3H]SR141716A, indicated the presence of the specific binding site. It may be concluded that in parotid glands the endogenous cannabinoid anandamide, bound to the CB1 cannabinoid receptor subtype, induces cAMP accumulation which in turn leads to amylase release and Na+-K+-ATPase inhibition.

Stimulation of guanylate cyclase in rat parotid membranes by phosphate

The natriuretic peptide receptor guanylate cyclases are members of the membrane-bound guanylate cyclase family. Atrial natriuretic pepticle (ANP) stimulates guanylate cyclase A, which is predominantly expressed in the rat parotid gland. ATP is well known to increase ANP-stimulated guanylate cyclase, with Mg2+ as a cofactor. We investigated the regulation of guanylate cyclase activity in rat parotid membranes with Mn2+ as a cofactor, because enzyme activity was much higher with Mn2+ than with Mg2+. ANP (10(-7)M) stimulated guanylate cyclase activity to 120%-130% of the control level, and ATP (0.1-1.0 mM) depressed its activity, with or without ANP, to 70%-80% of the control. Enzyme activity was increased by the addition of phosphate (5-20 mM). In the presence of phosphate (5 mM), guanylate cyclase with and without ANP was maximally stimulated to 5- and 6.6-fold of the control, respectively. The net stimulation of guanylate cyclase by ANP was increased at ATP concentrations between 0.2 and 0.5 mM in the presence of phosphate (5 mM or 10 mM), but no change was observed in the absence of phosphate. Phosphate not only stimulated guanylate cyclase in the absence of ATP but altered the ATP regulation of ANP-stimulated guanylate cyclase. The stimulation of guanylate cyclase by phosphate may depend on a peculiarity of rat parotid membranes.

Roles of Munc18-3 in amylase release from rat parotid acinar cells

Several "soluble N-ethylmaleimide-sensitive fusion protein attachment protein receptor" (SNARE) proteins have been identified in rat parotid acinar cells, including VAMP-2, syntaxin 4, and SNAP-23. Furthermore, an association between Munc18c (Munc18-3) and syntaxin 4 has been reported. However, the role of Munc18-3 in secretory granule exocytosis on parotid acinar cells remains unclear. In the present study, we investigated the role of Munc18-3 in rat parotid acinar cells. Munc18-3 was localized on the apical plasma membrane where exocytosis occurs and interacted with syntaxin 4. Anti-Munc18-3 antibody dose-dependently decreased isoproterenol (IPR)-induced amylase release from SLO-permeabilized parotid acinar cells. Furthermore, stimulation of the acinar cells with IPR induced translocation of Munc18-3 from the plasma membrane to the cytosol. Munc-18-3 was not phosphorylated by a catalytic subunit of protein kinase (PK) A but phosphorylated by PKC. Treatment of the plasma membrane with PKC but not PKA induced displacement of Munc18-3 from the membrane. The results indicate that Munc18-3 regulates exocytosis in the acinar cells for IPR-induced amylase release and that phosphorylation of Munc18-3 by PKA is not involved in the mechanism.

Cholinergic regulation of Na+-K+-ATPase activity in rat parotid gland: changes after castration

In this study, we investigated the different signalling pathways involved in muscarinic acetylcholine M(3) receptor-dependent modulation of Na(+)-K(+)-ATPase in parotid glands from normal and castrated rats. Carbachol inhibited the enzyme activity in parotid glands from control rats while it stimulated the enzyme activity in castrated rats. The inhibition of Ca(2+) calmodulin by trifluoperazine abolished the inhibitory effect of carbachol in control rats, while the inhibition of protein kinase C by staurosporine stimulated Na(+)-K(+)-ATPase. In castrated rats, trifluoperazine inhibited the carbachol-stimulant effect while staurosporine had no effect. Results indicate that in control glands the activation of a phospholipid-Ca(2+) calmodulin-dependent protein kinase C is responsible for the inhibitory effect of carbachol on Na(+)-K(+)-ATPase activity. In castrated rats, the activation of the enzyme by carbachol is regulated by its Ca(2+) calmodulin-stimulating action, and not by activation of protein kinase C. The activation of the Na(+)-K(+)-ATPase observed in castrated rats resulted in a decrease in carbachol-induced net K(+) efflux and thereby could decrease salivary fluid production.

Cytochemical detection of endogenous peroxidase in the intralobular ducts of hamster major salivary glands

Light and electron microscopic cytochemical investigation of endogenous peroxidase activity in the intralobular ducts of hamster major salivary glands was carried out using the diaminobenzidine-hydrogen peroxidase method. The peroxidase reaction product was localized in the nuclear envelope, the cisternae of the endoplasmic reticulum, the Golgi apparatus and secretory granules in both the intercalated duct cells and the striated duct light cells of all glands. These results suggest the ability of the intralobular duct cells to secrete peroxidase the same as that of acinar cells in hamster salivary glands.

Modulation by thyroid hormones of rat parotid amylase secretion stimulated by 5-hydroxytryptamine

The effects of 5-hydroxytryptamine (5-HT) upon amylase secretion by rat parotid glands were studied in three groups of animals: (a) intact control rats (euthyroid rats); (b) hypothyroid rats obtained by surgical thyroidectomy 2 wk before the experiments; and (c) hyperthyroid rats obtained by the administration of sodium l-triiodothyronine for 2 wk before the experiments. Hyperthyroid rats showed significantly higher baseline amylase release than control rats. When the glands were stimulated with 5-HT (30 micro m), amylase release was significantly lower in the hypothyroid group and higher in the hyperthyroid rats than in control group. Addition of cholinergic, adrenergic or substance P antagonists did not modify 5-HT-stimulated amylase activity. The effects of 5-HT were partly but significantly blocked by the addition of 10 micro m methysergide (HT1/2/7 receptor blocker) in the three groups of rats. In contrast, 10 micro m ketanserine (HT2A receptor blocker) partly blocked the response to 5-HT only in the hyperthyroid animals. It was concluded that 5-HT induces amylase secretion by rat parotid glands through specific serotoninergic receptors, and that thyroid status modulates the 5-HT effect.

Immunohistochemical demonstration of acidic mammalian chitinase in the mouse salivary gland and gastric mucosa

Acidic mammalian chitinase (AMCase) is the sole chitinolytic enzyme that has been identified thus far in the gastrointestinal tract of mammals. AMCase mRNA expression has been demonstrated in the salivary gland and stomach of mice and in the stomach of humans, while a bovine homologue of AMCase is produced in the liver and secreted into the blood. The present study using antibody raised against bovine AMCase demonstrates the cellular distribution of AMCase in salivary and gastric secretions at the protein level. Immunostaining using mouse tissues detected intense immunoreactivity for AMCase in serous-type secretory cells of the parotid gland and von Ebner's gland. Gastric chief cells, localized at the bottom of gastric glands, were also immunoreactive for AMCase. Electron-microscopically, the immunoreactivity was localized in granules in the apical cytoplasm of these secretory cells, and not in other structures. Western blot analysis confirmed the existence of AMCase in the parotid gland and stomach, and in their secretions in mice. However, no immunoreactive band was clearly detectable in immunoblots of the human parotid saliva and gastric juice. At least in the mouse, AMCase is secreted into the saliva and gastric juice, and may function as a digestive enzyme or play a defensive role against chitinous pathogens.

Detection and characterization of a rat parotid gland protein kinase that catalyzes phosphorylation of matured destrin at Ser-2

Destrin, an actin-binding protein, is partly phosphorylated at Ser-2 (numbering on the matured form) in the resting rat parotid gland, and beta-adrenergic or cholinergic stimulation of this gland induces its dephosphorylation. In this study, we searched for the protein kinase involved in phosphorylation of destrin. We developed an assay method for the kinase, using an antibody specific to destrin phosphorylated at Ser-2, and detected the kinase in the rat parotid homogenate. This enzyme was predominantly (93%) present in the soluble fraction, and the enzyme in this fraction was characterized. It had an optimum pH at 6.8 and required 3-5 mM Mg2+ for its maximum activity. Ca2+ (1 mM) had no effect whereas Mn2+ (5 mM) inhibited the enzyme activity by 75%. The apparent Km values for destrin and ATP were 92 microg/ml and 170 microM, respectively. GTP was an inefficient phosphate donor, and cAMP had no effect. Heat-denatured destrin was poorly phosphorylated. Two-dimensional PAGE analysis of destrin phosphorylated with the soluble fraction indicated that it was exclusively phosphorylated at Ser-2. None of the protein kinase inhibitors tested here was specific to this enzyme. At 1 mM, ML-7, Y-27632, KN-93, HA-1077, H-7, and H-8 inhibited the activity by 88, 61, 58, 49, 46, and 42%, respectively. Staurosporine (2 microM) and H-89 (50 microM) inhibited the activity by 48 and 33%, respectively. Heparin (30 microg/ml) had no effect. These results suggest that the rat parotid gland contains a novel, constitutively active, soluble protein kinase catalyzing specific phosphorylation of destrin at Ser-2.

Specific expression of an A-kinase anchoring protein subtype, AKAP-150, and specific regulatory mechanism for Na(+),K(+)-ATPase via protein kinase A in the parotid gland among the three major salivary glands of the rat

We have examined the expression of A-kinase anchoring protein (AKAP) in the three major salivary glands, i.e. the parotid gland (PG), submandibular gland (SMG), and sublingual gland (SLG), of the rat to elucidate the functional relevance between saliva secretion and Na(+),K(+)-ATPase regulation by protein kinase A (PKA)-dependent phosphorylation, since an AKAP subtype, AKAP-150, is known to be involved in the regulation of the ATPase in PG. Although AKAP-150 and its mRNA were clearly detected in the PG, they were hardly detectable in either the SMG or SLG. The membrane-bound form of the RII regulatory subunit of PKA, an index for the total amount of AKAP subtypes and therefore of the anchored PKA holoenzyme, was also undetectable in membranes from the SMG and SLG but was found in the PG; though a substantial and comparable amount of Na(+),K(+)-ATPase was present in all of these membrane preparations. Incubation with [gamma-32P]ATP revealed that Na(+),K(+)-ATPase in the PG membranes was quickly phosphorylated upon the addition of cAMP, whereas the ATPases in the membranes from SMG and SLG were not; though they were readily and equally phosphorylated by the exogenously added PKA catalytic subunit. AKAP-150 in the basolateral membranes of PG acinar cells was co-immunoprecipitated with RII by an anti-RII antiserum; and AKAP-150 and Na(+),K(+)-ATPase were immunohistochemically co-localized predominantly on the basolateral membranes, suggesting a possibility that the ATPase might directly interact with the AKAP to form an ATPase/AKAP/PKA complex or associate with the AKAP, such association being mediated via some scaffolding molecule. Expression of AKAP-150 and quick down-regulation of Na(+),K(+)-ATPase by AKAP-anchored PKA in response to cAMP elevation are characteristics specific to PG among the three major salivary glands, suggesting the presence of PG-specific regulatory mechanisms for saliva production/secretion.

Castration decreases amylase release associated with muscarinic acetylcholine receptor downregulation in rat parotid gland

1 The mechanism and receptor subtypes involved in carbachol-stimulated amylase release and its changes after castration were studied in parotid slices from male rats. 2 Carbachol induced both amylase release and inositol phosphate (IP) accumulation in parotid slices from control and castrated rats, but castration induced a decrease of carbachol maximal effect. The effect of castration was reverted by testosterone replacement. 3 The selective M(1) and M(3) muscarinic receptor antagonists, pirenzepine and 4-diphenylacetoxy-N-methylpiperidine methiodide, respectively, inhibited carbachol-stimulated amylase release and IP accumulation in a dose-dependent manner in parotid slices from control and castrated rats. 4 A diminution of binding sites of muscarinic receptor in parotid membrane from castrated rats was observed. Competition binding assays showed that both, M(1) and M(3) muscarinic receptor subtypes are expressed in membranes of parotid glands from control and castrated rats, M(3) being the greater population. 5 These results suggest that amylase release induced by carbachol in parotid slices is mediated by phosphoinositide accumulation. This mechanism appears to be triggered by the activation of M(1) and M(3) muscarinic receptor subtypes. Castration induced a decrease of the maximal effect of carbachol evoked amylase release and IP accumulation followed by a diminution in the number of parotid gland muscarinic acetylcholine receptors.

Immunohistochemical evidence of nNOS and changes after intraglandular application of botulinum toxin A in cephalic salivary glands of adult rats

The purpose of our study was to investigate the possible influence of local injections of botulinum toxin A on the activity of neuronal nitric oxide synthase (nNOS) in cephalic salivary glands of adult rats. The role of nitric oxide (NO) as a possible neuromodulator of vascular regulation and in particular regulation of secretion in the upper respiratory and aerodigestive tract is discussed. We present immunohistochemical evidence of nNOS in the salivary glands of female adult Wistar rats, both in native (untreated) glands and after intraglandular injection of botulinum toxin A under general anesthesia. Other than in the untreated glands, there was a significant decrease in nNOS in the treated organs which became stronger with extended toxin exposure time. After our laboratory had already shown a decrease in acetylcholinesterase immunoreactivity after injection of botulinum toxin A into the cephalic salivary glands of the rat, the present study discusses a possible participation of NO in the regulation of secretion from these organs. As a conclusion, it might be assumed that the influence of botulinum toxin A on nNOS in the cephalic salivary glands of the rat is able to explain the sometimes longer duration of the toxin effect at the neuroglandular junction than at the motor endplate.

Expression and localization of carbonic anhydrase in bovine mammary gland and secretion in milk

Little attention has been paid to carbonic anhydrase VI (CA VI), a secretory type isozyme, in the bovine mammary gland, although the gland is an important exocrine gland and CA VI is known to localize in exocrine glands such as salivary and lacrimal glands in various animal species. In the present study mRNA expression and protein localization of CA VI in isolated gland tissues and in cloned epithelial cells from the mammary gland of Holstein cows (Bos taurus) were observed by reverse transcript polymerase chain reaction and immunocytochemistry. Also, changes of CA VI concentrations in milk were measured for 2 months postpartum by an enzyme-linked immunosorbent assay. CA VI gene expression was detected in the gland tissues and epithelial cells, and CA VI protein was localized in the cytoplasm of the epithelial cells. Colostrum contained the highest concentration of CA VI protein (100 ng/ml), decreasing in an exponential manner (P<0.001). We conclude that bovine mammary epithelial cells synthesize and secrete CA VI in colostrum at higher concentration than in normal milk, implying its role to compensate for low CA VI secretion in neonatal calves.

Glycogen content and activities of enzymes involved in the carbohydrate metabolism of the salivary glands of rats during postnatal development

Carbohydrate metabolism was examined in the developing rat salivary glands by analysing enzymatic activity and glycogen content in the postnatal parotid and submandibular glands. The following enzymes of the carbohydrate metabolism, hexokinase (HK), phosphofructokinase-1 (PFK-1), pyruvate kinase (PK), glucose-6-phosphate dehydrogenase (G6PD), and lactate dehydrogenase (LDH) as well as the content of glycogen were determined in the salivary glands of rats aged 2, 7, 14, 21, 30 and 60 days. The specific activity of HK increased from days 2 to 21 and then it decreased up to 60 days old. The values found for the submandibular glands were from 2.5 to 4.9 times higher than those found for the parotid gland, except for rats aged 60 days. PFK-1 showed a different pattern of variation between the glands. In the submandibular gland there was a statistically significant increase in PFK-1 specific activity from 2 to 30 days of age and then, in the 60 days old group a return to level of the rats aged 2 days. In parotid gland, the specific activity of PFK-1 decreased between 2 and 7 days of age, from 7 to 14 days the specific activity increased markedly and from 14 to 60 days old it gradually decreased. The specific activity of PK followed the same pattern of variation in the submandibular and parotid glands, showing no great variation. The specific activity of LDH decreased from 2 to 60 days old in the submandibular glands. In the parotid glands the mean values for this enzyme were higher for the 2 days old group, and then decreased to remained more or less constant. The potential capacity of the pentose phosphate pathway was greater than that of glycolysis at early ages. The glycogen content showed similar variation in both glands. It was initially high and then decreased. In conclusion, our results on the activities of enzymes involved in carbohydrate metabolism in submandibular and parotid glands may be relevant to the initiation of saliva secretion in these animals.

Expression of DNase I in rat parotid gland and small intestine is regulated by starvation and refeeding

DNase I in rats is mainly expressed in the parotid gland and the small intestine and functions as a digestive enzyme. Male Wistar rats were deprived of food for 48 h, refed with nonpurified diet for 2 h and killed at 0, 0.33, 0.67, 1, 2, 6 or 12 h. The activity and mRNA of DNase I in the parotid gland and the small intestine were determined. We found that in rats that were not fed for 48 h there was accumulation of DNase I in the parotid gland but not in the small intestine. In the parotid gland, refeeding decreased DNase I activity (P < 0.05), perhaps due to an increase in secretion. The increase in DNase I mRNA probably resulted from the need for protein synthesis. However, in the small intestine, both the enzyme activity and the amount of mRNA were up-regulated by refeeding (P < 0.05). Exposing rats to food in a sealed transparent flask also caused a 2.5-fold increase in DNase I mRNA within 30 min in the parotid gland. These data suggested that the expression of rat parotid DNase I is up-regulated by feeding and that mastication is not essential for the regulation.

Ca2+-dependent protein kinase--a modulation of the plasma membrane Ca2+-ATPase in parotid acinar cells

Cross-talk between cAMP and [Ca(2+)](i) signaling pathways represents a general feature that defines the specificity of stimulus-response coupling in a variety of cell types including parotid acinar cells. We have reported recently that cAMP potentiates Ca(2+) release from intracellular stores, primarily because of a protein kinase A-mediated phosphorylation of type II inositol 1,4,5-trisphosphate receptors (Bruce, J. I. E., Shuttleworth, T. J. S., Giovannucci, D. R., and Yule, D. I. (2002) J. Biol. Chem. 277, 1340-1348). The aim of the present study was to evaluate the functional and molecular mechanism whereby cAMP regulates Ca(2+) clearance pathways in parotid acinar cells. Following an agonist-induced increase in [Ca(2+)](i) the rate of Ca(2+) clearance, after the removal of the stimulus, was potentiated substantially ( approximately 2-fold) by treatment with forskolin. This effect was prevented completely by inhibition of the plasma membrane Ca(2+)-ATPase (PMCA) with La(3+). PMCA activity, when isolated pharmacologically, was also potentiated ( approximately 2-fold) by forskolin. Ca(2+) uptake into the endoplasmic reticulum of streptolysin-O-permeabilized cells by sarco/endoplasmic reticulum Ca(2+)-ATPase was largely unaffected by treatment with dibutyryl cAMP. Finally, in situ phosphorylation assays demonstrated that PMCA was phosphorylated by treatment with forskolin but only in the presence of carbamylcholine (carbachol). This effect of forskolin was Ca(2+)-dependent, and protein kinase C-independent, as potentiation of PMCA activity and phosphorylation of PMCA by forskolin also occurred when [Ca(2+)](i) was elevated by the sarco/endoplasmic reticulum Ca(2+)-ATPase inhibitor cyclopiazonic acid and was attenuated by pre-incubation with the Ca(2+) chelator, 1,2-bis(o-aminophenoxy) ethane-N,N,N',N'-tetraacetic acid (BAPTA). The present study demonstrates that elevated cAMP enhances the rate of Ca(2+) clearance because of a complex modulation of PMCA activity that involves a Ca(2+)-dependent step. Tight regulation of both Ca(2+) release and Ca(2+) efflux may represent a general feature of the mechanism whereby cAMP improves the fidelity and specificity of Ca(2+) signaling.

Effect of extracellular magnesium on secretagogue-evoked amylase secretion in the isolated rat parotid gland segments

This study investigates the effect of perturbation of extracellular magnesium [Mg2+]o on basal and acetylcholine (ACh), noradrenaline (NA) and phenylephrine (PHE)-evoked amylase secretion from isolated rat parotid gland segments. Both zero (0 mM) and elevated (5 mM and 10 mM) [Mg2+]o can significantly (P < 0.05) inhibit basal and secretagogue-evoked amylase secretion compared to the responses obtained in normal (1.1 mM) [Mg2+]o. The inhibitory effect of zero [Mg2+]o was more pronounced compared 10 mM [Mg2+]o. A concentration of 5 mM, [Mg2+]o was less effective at a secretagogue concentration of 10(-5) M but more pronounced in inhibiting amylase secretion when the concentration of the secretagogue was reduced to 10(-6) M. The results indicate that both hypo and hypermagnesaemia are associated with reduced salivary amylase secretion and both conditions may be associated with 'the dry mouth syndrome'.

Expression and regulation of the gene for arginase I in mouse salivary glands: requirement of CCAAT/enhancer-binding protein alpha for the expression in the parotid gland

Arginase in salivary glands is potentially involved in the synthesis of proline, glutamate, and polyamines that play specific physiological roles in the glands, and also in depletion of arginine in the oral cavity to protect teeth from microorganisms. We detected protein and mRNA for the type I isoform of arginase in mouse salivary glands. Enzymes of the arginine-biosynthetic pathway were also detected. Immunohistochemical analysis revealed that arginase I was enriched in the striated duct, and was also present in the acinus, demilune and granulated duct. Mice with targeted disruption of the gene for C/EBPalpha, which is a transcription factor essential for expression of the arginase I gene in the liver, showed dramatically reduced immunoreactivity for arginase I in the parotid gland but not in the submandibular and sublingual glands. Therefore, C/EBPalpha is specifically required for expression of the arginase I gene in the parotid gland.

Differences in the regulatory mechanism of amylase release by rat parotid and submandibular glands

It is not known whether the mechanisms involved in amylase release in submandibular and parotid glands are similar. Here, the participation of different signalling pathways in amylase release by the parotid and submandibular glands of the male rat was compared by studying the secretory response after beta-adrenergic stimulation. The beta-adrenergic agonist isoproterenol induced an increase of cAMP in both salivary glands, but while in the parotid it triggered amylase release, in the submandibular it was unable to increase amylase secretion. Parotid amylase release was dependent on adenylate cyclase activation, as SQ-22536 inhibited the secretory effect. In contrast, submandibular amylase secretion did not depend on the intracellular concentration of cAMP, as SQ-22536 did not modify its secretory response. Moreover, other activators of adenylate cyclase, such as forskolin and prostaglandin E2, also failed to modify amylase release by the submandibular gland. Neither ionophores nor calcium-blocking agents, as well as calcium-calmodulin and nitric oxide synthase inhibitors, were effective in modifying basal amylase release by the submandibular gland. However, the disruption of microfilaments with cytochalasin B, but not the disruption of microtubules with colchicine, prevented amylase release in that gland. It is concluded that amylase exocytosis in the submandibular gland is a constitutive non-regulated phenomenon, as it is independent of extracellular or intracellular signals. It depends only on the integrity of the microfilaments, probably used by the vesicles to travel from the Golgi apparatus to the plasma membrane.

A restriction endonuclease assay for expression of human alpha-amylase isozymes

BACKGROUND

The alpha-amylase isozymes can be detected separately by electrophoresis; however, sometimes the identification is difficult because of their microheterogeneity. In the present study, we tried to establish a convenient method for the detection of alpha-amylase isozyme expression.

METHODS

The procedure is based on three different restriction sites presented in those genes; a PstI site in both AMY 2A and 2B genes, a HaeII site in both AMY 1 and 2A genes, and a BamHI site in AMY 2B gene. After amplification from total tissue RNAs by RT-PCR with primers that were able to cover each exon, the products were cleaved with corresponding restriction endonucleases.

RESULTS

This method was applied to human samples from the parotid gland, liver (non-hepatoma), hepatoma and white blood cells (WBCs). The results indicated that the parotid gland and hepatoma (also liver) clearly expressed AMY 1 and AMY 2B genes, respectively. However, AMY 2B gene was also expressed apparently in WBCs, which produced salivary-type isozyme of the alpha-amylase, although the amylase protein was not able to identify for the hepatic isozyme.

CONCLUSIONS

The method presented here might be convenient and useful for the determination of alpha-amylase isozyme expression in humans.

An enzyme histochemical and biochemical study of the activity of three oxidative enzymes in the developing rat parotid gland

Information on ductal differentiation in the developing rat parotid gland is sparse. One of the main functions of the striated and excretory ducts in this gland is the selective exchange of electrolytes from the primary fluid secreted by the acini. These ducts are rich in a number of enzymes involved in this task, suggesting that they might be useful as markers of ductal differentiation. The objective of this investigation was to delineate the developmental changes in activity of three of these, cytochrome C oxidase (CCO), succinate dehydrogenase (SDH), nicotinamide adenine phosphate dinucleotide (reduced form)-dehydrogenase (NADPH-DH). Histochemical localization of all three enzymes in fresh frozen sections was complemented by biochemical assays of CCO and SDH and cytochemical localization of CCO. Biochemically, CCO- and SDH-specific activity in gland homogenates increased progressively after birth, reaching adult levels at 21-28 days. Histochemically, deposits of reaction products of all three enzymes increased more in the striated and excretory ducts, especially in their basal cytoplasm, than in other glandular structures between 19 days in utero and 28 days after birth. During the same age span, the mitochondria in the striated and excretory ducts increased markedly in both number and size, migrated to a mostly basal location, and increased from many to virtually all showing strong cytochemical CCO reactions. These histochemical and cytochemical patterns of changes in enzyme activity at the cellular level accounted for the overall increases in CCO and SDH seen in the biochemical assays. Only the SDH histochemical reaction was consistently weak in the acini and intercalated ducts, and thus provided the most contrast with the progressively stronger reactions in the larger ducts. We conclude that of the three enzymes evaluated in these experiments, SDH is the best marker of the functional differentiation of the striated and excretory ducts in the developing rat parotid gland.

Effects of nutritional conditions around weaning on carbonic anhydrase activity in the parotid gland and ruminal and abomasal epithelia of Holstein calves

Thirty-two male Holstein calves were used to investigate the effects of nutritional conditions around weaning and aging on carbonic anhydrase (CA) activity in the parotid gland and epithelium from the rumen and abomasum. We fed calf starter and lucerne hay as well as milk replacer (group N) or fed milk replacer either with (group S) or without (group M) administration of short-chain fatty acids (SCFA) through polypropylene tubing into the forestomach until 13 weeks of age. The diets were fed at 1000 hours and 1600 hours, and SCFA were administrated after milk replacer feeding at 1600 hours. Slaughter and tissue sampling were carried out between 1300 hours and 1430 hours at 1, 3, 7, 13, and 18 weeks of age. Tissue samples from five adult (1.5-2.0 years-old) Holstein steers were obtained from a local abattoir. In group N, CA activity in the parotid gland gradually and significantly increased toward the adult value, whilst in the epithelium from the rumen and abomasum, adult values were reached at 3 and 7 weeks of age, respectively. At 13 weeks, the activity for group N was significantly higher than that for the other two groups in the parotid gland, but there was no significant difference in the epithelium from the rumen and abomasum. The concentration of the carbonic isozyme VI in the parotid gland also changed with age but, in contrast to CA activity, had not reached adult levels by 13 weeks of age. In groups M and S, parotid saliva did not show any change toward an alkaline pH or toward a reciprocal change in the concentrations between Cl(-) and HCO(3)(-), even at 13 weeks of age. From these results we conclude that a concentrate-hay based diet around weaning has a crucial role in CA development in the parotid gland, but not in the epithelium of the rumen and abomasum.

Comparison of amylase mRNAs from rat parotid gland, pancreas and liver using reverse transcriptase-polymerase chain reaction

The expression of mRNA for amylase was examined using the reverse transcriptase-polymerase chain reaction (RT-PCR). An amylase product was strongly detected in parotid and pancreas, but less strongly in liver. The degree of identity between the PCR products was assessed by restriction-enzyme mapping using two restriction enzymes, EcoRI and ScaI, and DNA sequencing. The PCR product from pancreas was cut by both EcoRI and ScaI, while the products from parotid and liver were cut by EcoRI but not by ScaI. The sequence of the parotid product was 90.4% homologous to that of the pancreas, and 100% homologous to that of the liver. These results indicate that the same amylase mRNA may be expressed in parotid and liver. In addition, the expression of amylase mRNAs in other rat tissues was investigated using RT-PCR, and the sensitivity of each PCR product to ScaI was tested. A weak single band was detected in submandibular gland, sublingual gland and stomach. ScaI digestion cut the stomach product into two fragments, but had no effect on the submandibular and sublingual products. Thus, it may be possible to classify amylase isoenzymes into pancreatic and parotid types based on the sensitivity of their PCR products to ScaI.

The effect of dietary consistency and water content on the parotid glands of submandibular and sublingual duct-ligated rats

The aim here was to estimate the significance of oral sensation and mastication on functional changes in the parotid glands of partially desalivated rats. Submandibular and sublingual duct-ligated and sham-operated control rats were fed three diets of similar chemical composition but different physical presentations. Two were solid, either pellets or powder, and one was liquid. Water and food intakes were similar for both the duct-ligated rats and sham-operated control rats when they ate the pelleted or powdered-diet, though more food was wasted by the duct-ligated rats in the powdered-diet group than in the pelleted-diet group. No food was wasted in the rats fed the liquid-diet. Parotid gland weight and amylase activity were greatest with the submandibular and sublingual duct-ligated rats fed the powdered-diet and smallest with the duct-ligated and sham-operated control rats fed the liquid-diet. The amount of food wasted correlated positively with the parotid gland weight and parotid amylase activity of the rats. These findings support the view that it is the contact of dry food with the oral mucosa rather than the jaw movements involved in mastication that increases parotid gland weight and amylase activity in partial desalivated rats.

Effect of extracellular magnesium on nerve-mediated and acetylcholine-evoked in vitro amylase release in rat parotid gland tissue

In this study the effects of changes in extracellular magnesium ([Mg(2+)](o)) and calcium ([Ca(2+)](o)) concentrations on basal and on nerve-mediated and acetylcholine (ACh)-evoked in vitro amylase release and calcium mobilization were investigated in rat parotid gland tissue. In the presence of a normal (2.56 mM) [Ca(2+)](o), both zero (0 mM) and an elevated (10 mM) [Mg(2+)](o) significantly attenuated basal and ACh-evoked amylase release compared to the response obtained in normal (1.1 mM) [Mg(2+)](o). During electrical field stimulation (EFS) of parotid tissues, only elevated [Mg(2+)](o) reduced amylase release. In a Ca(2+)-free medium, both basal and ACh-evoked amylase output were markedly reduced compared to the responses obtained under similar conditions in normal [Ca(2+)](o). Again, the ACh-induced amylase release in a Ca(2+)-free solution was larger in normal [Mg(2+)](o) than when the [Mg(2+)](o) was either zero or was elevated to 10 mM. Perturbation of [Mg(2+)](o) had no significant effect on basal intracellular free calcium concentration ([Ca(2+)](i)) in parotid acinar cells loaded with the fluorescent Ca(2+) indicator fura-2. Both zero Mg(2+) and an elevated [Mg(2+)](o) significantly reduced the ACh-induced rise in the peak and the plateau phase of the Ca(2+) transient that was seen in normal [Mg(2+)](o). In parotid acinar cells loaded with the fluorescent Mg(2+) indicator magfura-2, ACh elicited a gradual decrease in intracellular free Mg(2+) concentration ([Mg(2+)](i)) to below the basal level. The results indicate that both hypo- and hypermagnesaemia may reduce both basal and ACh-evoked amylase secretion from the salivary gland. As far as the ACh-evoked response is concerned, the effect may be exerted by a decrease in cellular Ca(2+) transport.