Lowered susceptibility of muscarinic receptor involved in salivary secretion of streptozotocin-induced diabetic rats

Expression and localization of adiponectin in myoepithelial cells in sublingual glands of normal and diabetic rats

OBJECTIVES

Adiponectin is a hormone produced by adipocytes with anti-atherosclerotic and anti-diabetic properties. We previously discovered that adiponectin is specifically localized in the myoepithelial cells of rat sublingual glands. This study aims to investigate the localization of adiponectin and its receptors, AdipoR1 and AdipoR2, in adult rats, postnatally developing rats, and diabetic model rats.

METHODS

We examined the localization and expression of adiponectin and its receptors by immunohistochemistry and RT-PCR in the sublingual glands of adult rats and in two diabetic rat models: Streptozotocin (STZ)-treated rats for type 1 diabetes and GK rats for type 2 diabetes.

RESULTS

In rat sublingual glands, adiponectin was localized in the cytoplasm of myoepithelial cells, while AdipoR1 and AdipoR2 were localized in the basolateral membrane of mucous acinar cells. In GK rats, there was a significant decrease in the immunoreactivity and mRNA levels of adiponectin, while both AdipoR1 and AdipoR2 expression levels were upregulated. In STZ-treated rats, both adiponectin and its receptors showed reduced expression.

CONCLUSIONS

Adiponectin acts as a paracrine factor in sublingual myoepithelial cells, influencing salivary secretion through upregulated receptors in acinar cells, particularly in type 2 diabetes. This process is associated with a reduction in myoepithelial adiponectin levels.

Gemigliptin Improves Salivary Gland Dysfunction in D-Galactose-Injected Aging Rats

Oral dryness is among the most common conditions experienced by the elderly. As saliva plays a crucial role in maintaining oral health and overall quality of life, the condition is increasingly taking its toll on a rapidly growing aging population. D-galactose (D-gal) stimulates their formation, which in turn cause oxidative stress and accelerate age-related decline in physical function. In this study, we observed a reduction in salivary secretion and amylase levels in aged rats injected with D-gal, confirming salivary gland dysfunction. Treatment with gemigliptin increased DPP-4 inhibition and GLP-1 levels in the salivary glands of aging rats and reduced the expression of AGEs and receptors for advanced glycation end products (RAGE). This effect was caused by the presence of additional reactive oxygen species (ROS) in the salivary glands of the examined rats. Gemigliptin's cytoprotective effect reduced amylase and mucin accumulation and increased AQP5 expression, which are important indicators of salivary gland function. In sum, gemigliptin was shown to improve D-gal-induced decline in the salivary gland function of aged rats through its anti-glycation and antioxidant activities. Gemigliptin shows promise as a treatment strategy for patients experiencing decreased salivary function associated with their advancing age.

Salivary gland proteins alterations in the diabetic milieu

Salivary glands are considered the chief exocrine glands of the mouth and physiologically contribute to the maintenance of the homeostasis of the oral cavity. They consist of the parotid, submandibular and sublingual glands, which come in pairs and are collectively called the major glands, and the minor glands, which are much smaller and are dispersed throughout the buccal cavity. Salivary glands are distinguished by their size, amount of saliva secretion and their location in the oral cavity. Salivary glands pathophysiology has been a subject of interest in various worldwide metabolic disorders, including diabetes mellitus. Diabetes mellitus (DM), a global health concern, with a pathological imprint involved in vasculature, promotes microvascular and macrovascular complications among which periodontitis ranks sixth. Indeed, DM has also been directly associated with oral health lesions. Specifically, salivary glands in the context of diabetes have been a focal point of study and emphasis in the research field. There is evidence that relates salivary secretion content and diabetes progression. In this review, we present all the reported evidence of the deregulation of specific salivary proteins associated with the progression of diabetes in parallel with changes in salivary gland morphology, cellular architecture, and salivary secretion and composition more generally.

Enhanced Salivary and General Oxidative Stress in Hashimoto's Thyroiditis Women in Euthyreosis

Hashimoto’s thyroiditis (HT) is one of the most common autoimmune diseases. Although HT is inextricably linked to oxidative stress, there have been no studies assessing salivary redox homeostasis or salivary gland function in patients with HT. This study is the first to compare antioxidant defense and oxidative stress biomarkers in non-stimulated (NWS) and stimulated (SWS) whole saliva and plasma/erythrocytes of HT patients compared to controls. The study included 45 women with HT in the euthyreosis period as well as an age- and gender-matched control group. We showed that NWS secretion was significantly lower in HT patients compared to healthy controls, similar to salivary amylase activity in NWS and SWS. Catalase and peroxidase activities were considerably higher in NWS and SWS of HT patients, while the concentrations of reduced glutathione and uric acid were significantly lower in comparison with healthy subjects. Total antioxidant potential was significantly lower, while total oxidant status and the level of oxidation products of proteins (advanced glycation end products, advanced oxidation protein products) and lipids (malondialdehyde, lipid hydroperoxides) were significantly higher in NWS, SWS and plasma of HT patients. In conclusion, in both salivary glands of women with HT in euthyreosis, the ability to maintain redox homeostasis was hindered. In HT patients we observed oxidative damage to salivary proteins and lipids; thus, some biomarkers of oxidative stress may present a potential diagnostic value.

Relationship between impaired parasympathetic vasodilation and hyposalivation in parotid glands associated with type 2 diabetes mellitus

We examined the relationship between hemodynamics in the three major salivary glands and salivary secretion in urethane-anesthetized and sympathectomized type 2 diabetic and nondiabetic rats via laser speckle imaging and by collecting the saliva. Lingual nerve stimulation elicited rapid increases in glandular blood flow and induced salivary secretion from the three glands in both diabetic and nondiabetic rats. In the parotid gland, the magnitude of blood flow increase and salivary secretion was significantly lower in the diabetic rats when compared with the nondiabetic rats; however, this was not observed in the other glands. Although the intravenous administration of acetylcholine increased blood flow in the parotid gland in a dose-dependent manner, the response was significantly lower in the diabetic rats when compared with the nondiabetic rats. Similarly, mRNA expression levels of M1 and M3 muscarinic acetylcholine receptors in the parotid gland were relatively lower in the diabetic rats compared with the nondiabetic rats. Our results indicate that type 2 diabetes impairs parasympathetic vasodilation and salivary secretion in the parotid gland and suggest that disturbances in the cholinergic vasodilator pathway may contribute to the underlying mechanisms involved in the disruption of parasympathetic nerve-mediated glandular vasodilation.

Antioxidant Defense, Oxidative Modification, and Salivary Gland Function in an Early Phase of Cerulein Pancreatitis

Acute pancreatitis (AP) is a multifactorial disease characterized by necroinflammatory changes of the pancreas. Our study is the first study which evaluated the relationship between the free radical production, enzymatic and nonenzymatic antioxidants, oxidative damage, and secretory function of the salivary glands of AP rats. Male Wistar rats were divided equally into 2 groups: control (n = 9) and AP (n = 9). AP was induced by intraperitoneal injection with cerulein and confirmed by higher serum amylase and lipase. We have demonstrated that the superoxide dismutase and glutathione reductase activities, as well as reduced glutathione concentration, were significantly decreased in both the parotid and submandibular glands of AP rats as compared to the control rats. The production of free radicals evidenced as dichlorodihydrofluorescein assay and the activity of NADPH oxidase and xanthine oxidase and IL-1β concentration were significantly higher in the parotid and submandibular glands of AP rats compared to the controls. In AP rats, we also showed a statistical increase in oxidation modification products (advanced glycation end products and advanced oxidation protein products), salivary amylase activity, and significant decrease in the total protein content. However, we did not show apoptosis and any morphological changes in the histological examination of the salivary glands of AP rats. To sum up, cerulein-induced AP intensifies production of oxygen free radicals, impairs the redox balance of the salivary glands, and is responsible for higher oxidative damage to these glands. Interestingly, oxidative modification of proteins and dysfunction of the antioxidant barrier are more pronounced in the submandibular glands of AP rats.

Hyperglycemia simultaneously induces initial caries development and enhances spontaneous occlusal surface wear in molar teeth related to parotid gland disorder in alloxan-induced diabetic rats

Diabetes and salivary gland dysfunction are major factors that induce dental caries in experimental animals, but there are no reports analyzing the association of dental caries and salivary glands in an animal model of diabetes mellitus (DM). To clarify the initial development of dental caries and preceding salivary gland disorder, we performed a histopathological analysis on teeth and salivary glands in diabetic Wistar rats 7 weeks after alloxan treatment (DM group) in comparison with nondiabetic rats (Non-DM group) and functional analysis on saliva secretion during the experimental period. Pilocarpine-induced salivary fluid secretion in diabetic rats gradually decreased with continuous hyperglycemia from immediately after alloxan treatment to the time of autopsy. Histopathologically, Oil Red O-positive lipid droplets accumulated in the acinar cells of the parotid gland. No tooth was stereoscopically defined as having dental caries in any of the rats in either group; however, the external appearance remarkably changed owing to occlusal wear in almost all molars in the DM group. The initial lesions of dental caries, appearing as micro-defects in dentin with bacterial colonization on the molar surface, were identified using histopathological analysis, and the incidence in the DM group was more than twice that in the Non-DM group. In conclusion, hyperglycemia simultaneously induces initial caries development and enhances spontaneous occlusal wear in molar teeth of Wistar rats 7 weeks after alloxan treatment. The parotid gland dysfunction caused by hyperglycemia may be mostly involved in the pathogenesis of occlusal wear as well as in dental caries in this diabetic model.

Oxidative Modification in the Salivary Glands of High Fat-Diet Induced Insulin Resistant Rats

Still little is known about the role of oxidative stress (OS) in the pathogenesis of the salivary gland dysfunction in the course of insulin resistance (IR). To induce IR rats was fed with a high fat diet (HFD) during 8 weeks. Stimulated and non-stimulated salivary flow rate, total protein, as well as oxidative damage markers: 4-HNE protein adduct, 8-isoprostanes (8-isoP), 8-hydroxy-D-guanosine (8-OHdG), advanced oxidation protein product (AOPP), and protein carbonyls (PC) were determined in the plasma and submandibular and parotid glands of IR and control rats. We have shown a significant decrease (45%) of the stimulated salivary flow rate, and in the total protein concentration in the parotid (35%) and submandibular (10%) glands of HFD IR as compared to the control rats. The level of 4-HNE protein adduct (15%) and 8-isoP (20%) in the submandibular glands of IR rats as well as total level of 4-HNE protein adduct (39%), 8-isoP (27%), AOPP (25%), PC (32%), and 8-OHdG (18%) in the parotid glands of IR rats were significantly higher as compared to the control group. We showed no correlation between the assessed OS parameters in the plasma and salivary glands. However, the redox balance in both glands shifted toward the oxidative status, parotid glands of IR rats are exposed to greater intensity OS. Stimulated secretory ability and mechanisms involved in the synthesis/secretion of proteins in the salivary glands are depressed in the course of IR. Oxidative damage in the salivary glands arises independently from the general OS in the course of insulin resistance induced by a high fat diet.

Rebamipide, an anti-ulcerative drug, inhibits induction of salivary dysfunction by benzodiazepines

OBJECTIVES

The purpose of this study was to determine whether rebamipide, an antistomach ulcer agent, ameliorated benzodiazepine-induced hyposalivation in rat parotid gland (PG) and submandibular gland (SMG).

METHODS

Saliva was collected from PG and SMG through a capillary cannula inserted into the parotid duct and sublingual papillae, respectively, every 15 min for 1 h after stimulation with pilocarpine dissolved in physiological saline and intraperitoneally administered at 1 mg kg^-1 . Diazepam (DZP) was administered intraperitoneally at a dose of 0.2 mg kg^-1 twice daily for 7 days. Rebamipide was administered at 10, 20, 30, or 100 mg kg^-1 concomitantly with DZP to determine its effect on hyposalivation. The effect of rebamipide on movement of intracellular calcium ([Ca²⁺ ]i) in isolated parotid acinar cells was analyzed using Fluo4, a fluorescent dye used to detect Ca²⁺ .

RESULTS

Repetitive administration of DZP decreased salivary secretion in PG and SMG. This inhibitory effect was weakened by administration of rebamipide. Prior administration of DZP (10^-6 M) significantly suppressed carbachol (10^-7 M)-induced increase in [Ca²⁺ ]i. This inhibitory effect was ameliorated by combined use with rebamipide (5 × 10^-4 M).

CONCLUSION

This findings suggest that rebamipide weakens the downregulatory effect of DZP on salivary secretion by preventing DZP-induced suppression of increase in [Ca²⁺ ]i.

Rat submandibular gland perfusion method for clarifying inhibitory regulation of GABAA receptor

GABA is an inhibitory transmitter found in rat salivary gland. However, the inhibitory potential of GABA on salivary secretion is unclear. Using an in vivo cannulation method, intraperitoneal administration of GABA was ineffective in the absence of gabaculine, a GABA transaminase inhibitor, on pilocarpine-induced salivary secretion, suggesting that GABA was rendered metabolically inactive before reaching the salivary gland. We hypothesized that the action of a drug on the salivary glands could be measured directly using a submandibular gland perfusion system. The submandibular gland artery, veins, and duct were cannulated in situ so that physiological functions such as innervation would not be compromised. Hank's balanced salt solution (pH 7.4) was perfused at a rate of 0.5 ml/min together with 1 μM carbachol (CCh) over a 5-min period every 30 min. Amount of secreted saliva showed no change to the recurrent addition of CCh to the perfusate. GABA or muscimol dose-dependently inhibited CCh-induced salivary secretion. This effect was blocked by bicuculline, a GABA(A)-receptor (GABA(A)-R) antagonist, and enhanced by clonazepam, a central-type benzodiazepine-receptor agonist. These results suggest that salivary secretion is suppressed by GABA(A)-R in rat salivary gland and that the perfusion method used was effective in clarifying inhibitory regulation of GABA(A)-R.

Laser irradiation affects enzymatic antioxidant system of streptozotocin-induced diabetic rats

The aim of the present study was to analyze the effect of low-power laser irradiation in the antioxidant enzymatic system of submandibular (SMG) and parotid (PG) salivary glands of streptozotocin-induced diabetic rats. The animals were randomly divided into six groups: three diabetic groups (D0, D5, and D20) and three non-diabetic groups (C0, C5, and C20), according to laser dose received (0, 5, and 20 J/cm(2), respectively). Areas of approximately 1 cm(2) were demarcated in the salivary glands (each parotid and both submandibular glands) and after irradiated according to Simões et.al. (Lasers Med Sci 24:202-208, 2009). A diode laser (660 nm/100 mW) was used, with laser beam spot of 0.0177 cm(2). The group treated with 5 J/cm(2) laser dose was subjected to irradiation for 1 min and 4 s (total irradiation time) and the group treated with 20 J/cm(2) laser dose was subjected to irradiation for 4 min and 16 s. Twenty-four hours after irradiation the animals were euthanized and the salivary glands were removed for biochemical analysis. The total antioxidant values (TA), the activity of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase enzymes were determined. SOD and CAT activities, as well as TA were higher in SMG of irradiated diabetic rats. However, in SMG of non-diabetic rats, laser irradiation decreased TA values and led to an increase in the CAT activity. In addition, there was a decrease in the activity of CAT in PG of diabetic and non-diabetic animals after laser irradiation. According to the results of the present study, low-power laser irradiation can affect the enzymatic antioxidant system of salivary glands of streptozotocin-induced diabetic rats.

Hyperglycemia and xerostomia are key determinants of tooth decay in type 1 diabetic mice

Insulin-dependent type 1 diabetes mellitus (DM) and oral diseases are closely interrelated. Poor metabolic control in diabetics is associated with a high risk of gingivitis, periodontitis and tooth loss. Salivary flow declines in diabetics and patients suffer from xerostomia. Reduced saliva predisposes to enamel hypomineralization and caries formation; however, the mechanisms that initiate and lead to progression of tooth decay and periodontitis in type 1 DM have not been explored. To address this issue, we analyzed tooth morphology in Akita ⁻/⁻ mice that harbor a point mutation in the Ins2 insulin gene, which leads to progressive hyperglycemia. Mandibles from Akita ⁻/⁻ and wild-type littermates were analyzed by microCT, scanning EM and histology; teeth were examined for amelogenin (Amel) and ameloblastin (Ambn) expression. Mice were injected with pilocarpine to assess saliva production. As hyperglycemia may alter pulp repair, the effect of high glucose levels on the proliferation/differentiation of cultured MD10-F2 pulp cells was also analyzed. Results showed that Akita ⁻/⁻ mice at 6 weeks of age showed chalky white incisors that correlated with marked hyperglycemia and impaired saliva production. MicroCT of Akita ⁻/⁻ teeth revealed excessive enamel wearing and hypomineralization; immunostaining for Amel and Ambn was decreased. A striking feature was invasion of dentinal tubules with Streptococcus mitis and microabcesses that originated in the coronal pulp and progressed to pulp necrosis and periapical periodontitis. High levels of glucose also inhibited MD10-F2 cell proliferation and differentiation. Our findings provide the first evidence that hyperglycemia in combination with reduced saliva in a model of type1 DM leads to decreased enamel mineralization/matrix proteins and predisposes to excessive wearing and decay. Importantly, hyperglycemia adversely affects enamel matrix proteins and pulp repair. Early detection and treatment of hyperglycemia and hyposalivation may provide a useful strategy for preventing the dental complications of diabetes and promoting oral health in this population.

Sialic acid reduction in the saliva of streptozotocin induced diabetic rats

OBJECTIVE

Diabetes causes changes in the salivary glands and in the composition of saliva, as well as symptoms such as dry mouth and hyposalivation. Therefore, this study aimed at investigating changes in salivary secretion and composition, in response to parasympathetic stimuli, in diabetic rats induced with streptozotocin.

DESIGN

Diabetes was induced by a single intraperitoneal injection of streptozotocin. Thirty days after diabetes induction, the animals were anaesthetized and salivation was stimulated by an intraperitoneal injection of Pilocarpine (0.6mg/kg body weight) dissolved in distilled water. Saliva was collected for 40min and immediately stored at -80°C until analysis. The salivary flow rate, amount of total protein, amylase and peroxidase activities, and free and total sialic acid contents were measured.

RESULTS

Salivary flow rate was reduced in the diabetic group (p<0.05). Moreover, increases in total protein amount and in amylase and peroxidase activities were observed in diabetic animals. No difference was observed for free sialic acid content between groups. On the other hand, a significantly decrease in the total sialic acid content was observed in the diabetic group (p<0.05).

CONCLUSIONS

Our findings suggest that a decrease in sialic acid in the saliva of diabetic animals can be related to xerostomia reported by diabetic patients. However, further clinical trials are needed to verify if the decrease in sialic acid also occurs in human saliva.

Impairment of acetylcholine-mediated endothelium-dependent relaxation in isolated parotid artery of the alloxan-induced diabetic rabbit

The aim of this study was to assess the effect of type 1 diabetes mellitus (induced by a single intravenous injection of 100 mg kg(-1) of alloxan) on acetylcholine (ACh)-induced relaxation in isolated rabbit parotid gland feeding artery. Isometric force measurements and quantification of inducible nitric oxide synthase (iNOS) mRNA by real-time RT-PCR were made in parotid artery rings from diabetic and control rabbits. Acetylcholine induced concentration- and endothelium-dependent vasorelaxation that was significantly decreased in parotid artery rings from diabetic rabbits. Schild analysis of the ACh vasorelaxant effect, in the presence of selective muscarinic receptor antagonists, revealed involvement of the M(3) receptor subtype in parotid artery rings from both control and diabetic rabbits, with no change in antagonist affinity constants. The inhibitory effects of indomethacin, a non-selective inhibitor of cyclooxygenase, and of high potassium, an inhibitor of hyperpolarization, on ACh vasorelaxation were increased. The effect of N(G) -nitro-l-arginine, a non-selective inhibitor of NOS, was decreased in diabetes. S-methylisothiourea, a selective inhibitor of iNOS, significantly reduced ACh vasorelaxation only in parotid artery rings from diabetic rabbits. Also, up-regulation of iNOS mRNA expression was detected in parotid artery rings from diabetic rabbits. These results suggest that in parotid artery rings from diabetic rabbits, impaired endothelium-dependent vasorelaxation to ACh appears to be caused by the loss of a nitric oxide-mediated component and increased iNOS expression, and is unlikely to be caused by a change at the M(3) receptor level.

Abnormal subcellular localization of AQP5 and downregulated AQP5 protein in parotid glands of streptozotocin-induced diabetic rats

BACKGROUND

The mechanisms underlying diabetic xerostomia have not been clarified in relation with aquaporin-5 (AQP5) subcellular localization in salivary glands.

METHODS

Western blotting, real-time PCR, and immunocytochemistry were used to analyse AQP5 protein levels and mRNA expression. AQP5 protein levels were measured in the apical plasma membrane (APM) and detergent-insoluble fraction prepared from streptozotocin-diabetic rat parotid glands.

RESULTS

Despite an increase in AQP5 mRNA, AQP5 protein levels were decreased in diabetic parotid glands compared with controls. Immunohistochemical studies indicated that AQP5, under unstimulated conditions, colocalised with flotillin-2 and GM1 with a diffuse pattern in the apical cytoplasm of acinar and duct cells in both control and diabetic rats. Ten minutes after intravenous injection of muscarinic agonist cevimeline, AQP5 was dramatically increased together with flotillin-2 and GM1 in the APM of parotid acinar and duct cells of control but not diabetic rats. Sixty minutes after injection, AQP5 was located in a diffuse pattern in the apical cytoplasm in both rats. Treatment of the parotid tissues with cevimeline for 10min increased the Triton X-100 solubility of AQP5 in control but not diabetic rats. Administration of insulin to diabetic rats tended to restore the cevimeline-induced translocation of AQP5.

CONCLUSION

Lack of AQP5 translocation in the salivary gland in response to a muscarinic agonist and downregulation of AQP5 protein might lead to diabetic xerostomia.

GENERAL SIGNIFICANCE

Cevimeline is useful to cure diabetic xerostomia under insulin administration.

Diazepam enhances production of diazepam-binding inhibitor (DBI), a negative saliva secretion regulator, localized in rat salivary gland

Peripheral-type benzodiazepine receptor (PBR) and central-type benzodiazepine receptor (CBR) in salivary gland play a role in the inhibitory regulation of salivary secretion in rodents. Diazepam-binding inhibitor (DBI), an endogenous ligand for PBR, produces neurosteroids, which modulate CBR activity. In this study, we investigated the effect of repetitive administration of diazepam (DZP) on salivary secretion and expression of DBI mRNA and peptide. Moreover, mRNA expression of PBR and pituitary adenylate cyclase-activating polypeptide (PACAP), a transcriptional regulator for DBI promoter, was evaluated after repetitive administration of DZP. Repetitive administration, but not single administration, of 0.4 mg/kg DZP caused inhibition of salivary secretion and enhanced expression of DBI, PACAP, and PBR mRNA in rat salivary gland, with an increase in production of DBI peptide. These results suggest that repetitive administration of DZP stimulates DBI production, which may result in an increase in the suppressive effect of DZP on salivary secretion.

The mechanism of protracted wound healing on oral mucosa in diabetes. Review

Diabetic patients increase their body's susceptibility to infection and diabetes is a risk factor for periodontal diseases and oral infection. Although many studies showed the mechanism of impaired wound healing in diabetes, there are still arguments to shed light on what kind of factors, including local and systemic factors are involved in the protracted wound healing. This review article summarizes reports on the wound healing in diabetes and discusses the mechanism of the protracted wound healing of the oral mucosa in diabetes. Delayed vascularization, reduction in blood flow, decline in innate immunity, decreases in growth factor production, and psychological stresses may be involved in the protracted wound healing of the oral mucosa in diabetics.

Astaxanthin restores the enzymatic antioxidant profile in salivary gland of alloxan-induced diabetic rats

OBJECTIVE

To evaluate the effect of astaxanthin on antioxidant parameters of salivary gland from diabetic rats. The hypothesis of the study was whether the supplementation of diabetic rats with astaxanthin might antagonize, or at least prevent, the defect in their antioxidative status.

DESIGN

Wistar rats (n=32) were divided in 4 groups: untreated control, treated control, untreated diabetic and treated diabetic rats. Astaxanthin (20mg/kg body weight) was administered daily by gavage for 30 days. On day 23, diabetes was induced by injection of alloxan (60 mg/kg body weight). After 7 days of diabetes induction, the rats were killed and submandibular and parotid removed. Superoxide dismutase (SOD), catalase, glutathione peroxidase and reductase activities and the content of thiol groups were determined. Data were compared by ANOVA and the Tukey test (p<0.05).

RESULTS

Diabetes caused a reduction of SOD, and thiol content and increase of catalase and glutathione peroxidase activities of submandibular gland whilst in the parotid gland diabetes caused an increase of thiol content and no effect in the antioxidant system. The astaxanthin restores the enzymatic activities in the salivary gland, however does not prevent its oxidative damage.

CONCLUSION

The submandibular gland presented more susceptibility to oxidative alterations induced by diabetes. Astaxanthin presented a positive effect on the oxidative protection of the salivary gland from diabetic rats.

Expression of BMP7 is associated with resistance to diabetic stress: comparison among mouse salivary glands

We determined mRNA levels of bone morphogenetic protein 7 (BMP7), a growth and differentiation factor belonging to the transforming growth factor-beta superfamily, in the salivary glands of mice with streptozotocin (200 mg/kg, i.p.)-induced diabetes. We also examined the effects of BMP7 on secretion of saliva and degenerative change in salivary glands in diabetic mice. In normal mice, BMP7 mRNA levels were high in the submandibular gland and low in the parotid gland, while in diabetic mice, levels were significantly decreased in the parotid gland, but not in the submandibular gland. No significant difference was observed in mRNA levels of BMP receptors between normal and diabetic mice. In diabetic mice, pilocarpine (4 mg/kg, i.p.)-stimulated salivary secretion showed a remarkable decrease in both parotid and submandibular gland, although degree of reduction was smaller in the latter. Notable degeneration with vacuolation and atrophy was also found in parotid gland, whereas degeneration of submandibular gland was slight. Administration of BMP7 (50 and 100 microg/kg, i.v.) in diabetic mice induced a significant increase in salivary secretion, with rate of recovery higher in parotid gland than in submandibular gland. In diabetic mice, BMP7 also exhibited a powerful protective effect in degenerated salivary gland, especially in parotid gland. These results suggest that BMP7 acts to prevent diabetic damage in salivary gland, and that its cytoprotective effect is closely correlated with mRNA levels in tissue.

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.

Changes in functioning of rat submandibular salivary gland under streptozotocin-induced diabetes are associated with alterations of Ca2+ signaling and Ca2+ transporting pumps

Xerostomia and pathological thirst are troublesome complications of diabetes mellitus associated with impaired functioning of salivary glands; however, their cellular mechanisms are not yet determined. Isolated acinar cells were loaded with Ca2+ indicators fura-2/AM for measuring cytosolic Ca2+ concentration ([Ca2+]i) or mag-fura-2/AM-inside the endoplasmic reticulum (ER). We found a dramatic decrease in pilocarpine-stimulated saliva flow, protein content and amylase activity in rats after 6 weeks of diabetes vs. healthy animals. This was accompanied with rise in resting [Ca2+]i and increased potency of acetylcholine (ACh) and carbachol (CCh) but not norepinephrine (NE) to induce [Ca2+]i transients in acinar cells from diabetic animals. However, [Ca2+]i transients mediated by Ca2+ release from ER stores (induced by application of either ACh, CCh, NE, or ionomycin in Ca2+-free extracellular medium) were decreased under diabetes. Application of inositol-1,4,5-trisphosphate led to smaller Ca2+ release from ER under the diabetes. Both plasmalemma and ER Ca2+-ATPases activity was reduced and the latter showed the increased affinity to ATP under the diabetes. We conclude that the diabetes caused impairment of salivary cells functions that, on the cellular level, associates with Ca2+ overload, increased Ca2+-mobilizing ability of muscarinic but not adrenergic receptors, decreased Ca2+-ATPases activity and ER Ca2+ content.

Stereology and ultrastructure of the salivary glands of diabetic Nod mice submitted to long-term insulin treatment

Insulin-dependent diabetes mellitus compromises the salivary glands, altering their morphology and the mechanisms of salivation, which are fundamental for oral health. Thus, the aim of the present study was to determine the effects of prolonged insulin treatment on the morphology of the salivary glands in Nod mice. Forty-five female mice were divided into five groups: nine positive diabetic Nod mice for 10 days (group 1), nine positive diabetic Nod mice for 20 days (group 2), nine diabetic Nod mice for 10 days (group 3), nine diabetic Nod mice for 20 days (group 4), and nine nondiabetic BALB/c mice (group 5). Animals of groups 3 and 4 received 4-5 U of insulin daily, whereas animals of groups 1, 2, and 5 received the same dose of physiological saline simulating the experimental conditions. Samples of the salivary glands were analyzed by light, transmission, and scanning electron microscopies. The results showed intense alterations in diabetic animals characterized by nuclear and cytoplasmic atrophy, biomembrane disorganization, an increase in fibrillar components of the extracellular matrix, and the presence of inflammatory cells. Insulin treatment exerted positive effects on the recovery of the changes resulting from the diabetic state in both parotid and submandibular glands but the pattern continued to be altered. It can be concluded that, in addition to compromising the processes of tissue maintenance and renewal, tissue destructuring leads to alterations in functional mechanisms in both diabetic animals and animals submitted to glycemic control.

Molecular Mechanisms and Drug Development in Aquaporin Water Channel Diseases: The Translocation of Aquaporin-5 From Lipid Rafts to the Apical Plasma Membranes of Parotid Glands of Normal Rats and the Impairment of It in Diabetic or Aged Rats

Salivary secretion from rat salivary glands occurs in response to stimulation by acetylcholine and norepinephrine released from nerve endings. Aquaporin-5 (AQP5) localizes in lipid rafts under control conditions and is induced to traffic to the apical plasma membrane in interlobular ducts of rat parotid glands by the activation of M3 muscarinic acetylcholine receptors or alpha1-adrenoceptors. This review will focus on the mechanisms of the translocation of AQP5 from lipid rafts to the apical plasma membrane in the interlobular duct cells of parotid glands of normal rats and the impairment of its translocation in diabetic or senescent rats.

Muscarinic receptors: What we know

An understanding of muscarinic receptors is tantamount to an understanding of overactive bladder. The M(3) muscarinic receptor subtype is responsible for detrusor smooth muscle contraction and it exerts an exocrine function in the salivary glands. Alterations in the receptor's response to acetylcholine as a result of injury may lead to hypersensitivity and overactivity. The M(2) receptor subtype, which is mainly responsible for cardiac function, is the muscarinic receptor of highest proportion in the detrusor. M(2) also may play a role in detrusor contraction in injury and pathologic states. Muscarinic antagonists are the mainstay of pharmacotherapy for overactive bladder, but those that are available are not tissue specific. Growing knowledge of the nuances of receptor-ligand behavior and interaction between muscarinic receptors subtypes may provide novel targets for future drug development, improve efficacy, and reduce bothersome side effects.

Dysfunction of aorta involves different patterns of intracellular signaling pathways in diabetic rats

Rat models of insulin-dependent (streptozotocin-induced) and independent (Otsuka Long-Evans Tokushima Fatty (OLETF)) diabetes had sustained and transient increases in blood glucose levels. Over-contraction due to norepinephrine was seen exclusively in streptozotocin rat aorta. Contraction was enhanced under high-glucose conditions in OLETF rats. In order to understand the association between these patterns of changes, total diacylglycerol was measured as a key element of phosphatidylinositol-turnover due to the conversion of some incorporated glucose into diacylglycerol. Streptozotocin rats had enhanced basal diacylglycerol. Both diacylglycerol kinase (metabolic enzyme of diacylglycerol) and total phosphatidylinositol turnover activities also increased on norepinephrine stimulation, independent of extracellular glucose level. On the other hand, diacylglycerol, diacylglycerol kinase and phosphatidylinositol turnover in OLETF rats increased under high glucose conditions in the absence of norepinephrine treatment. These results indicated that diacylglycerol and diacylglycerol kinase-mediated phosphatidylinositol turnover acceleration was influenced by an increase in glucose levels in OLETF rats or by receptor-mediated signals in streptozotocin rats including glucose desensitization based on submaximal incorporation. We suggest that the alteration of vascular dysfunction is induced by different factors in each type of diabetes.