Inhibitory effect of diazepam on muscarinic receptor-stimulated inositol 1,4,5-trisphosphate production in rat parotid acinar cells

Effect of propofol on salivary secretion from the submandibular, sublingual, and labial glands during intravenous sedation

Background

Recent animal studies have suggested the role of GABA type A (GABA-_A) receptors in salivation, showing that GABA-_A receptor agonists inhibit salivary secretion. This study aimed to evaluate the effects of propofol (a GABA-_A agonist) on salivary secretions from the submandibular, sublingual, and labial glands during intravenous sedation in healthy volunteers.

Methods

Twenty healthy male volunteers participated in the study. They received a loading dose of propofol 6 mg/kg/h for 10 min, followed by 3 mg/kg/h for 15 min. Salivary flow rates in the submandibular, sublingual, and labial glands were measured before, during, and after propofol infusion, and amylase activity was measured in the saliva from the submandibular and sublingual glands.

Results

We found that the salivary flow rates in the submandibular, sublingual, and labial glands significantly decreased during intravenous sedation with propofol (P < 0.01). Similarly, amylase activity in the saliva from the submandibular and sublingual glands was significantly decreased (P < 0.01).

Conclusion

It can be concluded that intravenous sedation with propofol decreases salivary secretion in the submandibular, sublingual, and labial glands via the GABA-_A receptor. These results may be useful for dental treatment when desalivation is necessary.

[Anticholinergic scales: Use in psychiatry and update of the anticholinergic impregnation scale]

Anticholinergic properties are well known to prescribers, notably in mental health, as a therapeutic strategy for i.e. extrapyramidal syndrome but also as a source of numerous adverse side effects. Herein, we propose a narrative literature review describing: (i) cholinergic pharmacology and anticholinergic properties; (ii) the importance of anticholinergic therapeutic properties in psychiatry; (iii) the existing anticholinergic drug scales and their usage limitations in Psychiatry and; last (iv) an update to the anticholinergic drug impregnation scale, designed for the French psychiatry practice. The anticholinergic side effects can appear both in the peripheral level (dry mouth, constipation, etc.) and in the central level (especially as cognitive deficits). Many of the so called « anticholinergic » drugs are in fact entirely or mostly antimuscarinic and act essentially as parasympathetic system antagonists. Overall, anticholinergic/antimuscarinic side effects are usually attributed to psychotropic medications: to certain antipsychotics, notably classical neuroleptics such as phenothiazine and also to tricyclic antidepressants. In practice, the impact of anticholinergic toxicity treatments is often highlighted due to their excessively prolonged use in patients on antipsychotics. Interestingly, these antipsychotic treatments are better known for their anticholinergic side effects, especially cognitive ones, with an early onset specially in elder patients and/or in the case of polymedication. In order to evaluate anticholinergic side effects, metrics known as anticholinergic burden scales were created in the last few decades. Nowadays, 13 different scales are documented and accepted by the international academic community, but only three of them are commonly used: the Anticholinergic Drug Scale (ADS), the Anticholinergic Risk Scale (ARS) and the Anticholinergic Burden Scale (ACB). All of them are based on a similar principle, consisting of grading treatments individually, and they are normally scored from 0 - no presence of side effects - to 3 - anticholinergic effects considered to be strong or very strong. Using these scales enables the calculation of the so-called "anticholinergic burden", which corresponds to the cumulative effect of using multiple medications with anticholinergic properties simultaneously. The application of anticholinergic scales to patients with psychiatric disorders has revealed that schizophrenic patients seem to be especially sensitive to anticholinergic cognitive side effects, while elder and depressed patients were more likely to show symptoms of dementia when exposed to higher anticholinergic burden. Unfortunately, these tools appear to have a low parallel reliability, and so they might induce large differences when assessing side effects predictability. In addition, the capacity of these scales to predict central adverse effects is limited due to the fact they poorly or do not differentiate, the ability of treatments to cross the blood-brain barrier. Finally, one last limitation on the validity of these scales is prescription posology is not accounted for side effects considered to be dose dependent. Recently, the MARANTE (Muscarinic Acetylcholine Receptor ANTagonist Exposure) scale has incorporated an anticholinergic burden weighting by posology. Nevertheless, this new model can be criticized, due to the limited number of medications included and due to testing a limited number of potency ranges and dosages for each treatment. Herein, we propose an update to the Anticholinergic Impregnation Scale, developed specifically for the French Psychiatry practice. The scale validation was based on an evaluation of the prescriptions correcting anticholinergic peripheral side effects (constipation, xerostomia and xeropthalmia). This indirect evaluation allowed us to show patients with an anticholinergic impregnation score higher than 5 received significantly more treatments for constipation and xerostomia. This strategy bypasses the bias of a cognitive evaluation in patients with severe mental health disorders. Moreover, the relevance of a tool developed specifically for French psychiatry is justified by the fact that some highly prescribed treatments for mental illness in France (cyamemazine and tropatemine) are strong anticholinergics, and also by the fact they are rarely included in the existing anticholinergic scales. This update of the original scale, published in 2017, includes information whether prescribed drugs cross the blood-brain barrier and thus makes possible a more accurate assessment when evaluating anticholinergic central side effects. Finally, the anticholinergic impregnation scale will soon be integrated into a prescription help software, which is currently being developed to take into consideration dose dependent adverse effects.

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.

Effects of Benzodiazepines on Acinar and Myoepithelial Cells

Background: Benzodiazepines (BZDs), the most commonly prescribed psychotropic drugs with anxiolytic action, may cause hyposalivation. It has been previously shown that BZDs can cause hypertrophy and decrease the acini cell number. In this study, we investigated the effects of BZDs and pilocarpine on rat parotid glands, specifically on acinar, ductal, and myoepithelial cells.

Methods: Ninety male Wistar rats were divided into nine groups. Control groups received a saline solution for 30 days (C30) and 60 days (C60), and pilocarpine (PILO) for 60 days. Experimental groups received lorazepam (L30) and midazolam (M30) for 30 days. Another group (LS60 or MS60) received lorazepam or midazolam for 30 days, respectively, and saline for additional 30 days. Finally, other groups (LP60 or MP60) received either lorazepam or midazolam for 30 days, respectively, and pilocarpine for additional 30 days. The expression of calponin in myoepithelial cells and the proliferating cell nuclear antigen (PCNA) in acinar and ductal cells were evaluated.

Results: Animals treated with lorazepam showed an increase in the number of positive staining cells for calponin as compared to control animals (p < 0.05). Midazolam administered with pilocarpine (MP60) induced an increase in the proliferation of acinar and ductal cells and a decrease in the positive staining cells for calponin as compared to midazolam administered with saline (MS60).

Conclusion: We found that myoepithelial cells might be more sensitive to the effects of BZD than acinar and ductal cells in rat parotid glands.

Modulation of benzodiazepine receptor, adrenoceptor and muscarinic receptor by diazepam in rat parotid gland

This study investigated the influence of diazepam on the binding characteristics of adrenoceptor, muscarinic and benzodiazepine receptors in rat parotid gland membrane using a radioligand binding assay. At a concentration of >10(-6)M, diazepam competed with [(3)H]dihydroalprenolol for β-adrenoceptor, but not [(3)H]prazosin for α-adrenoceptor or [(3)H]quinuclidinyl benzilate for muscarinic receptor. Continuous administration of diazepam at doses of 0.4mg/kg/day, i.p. for 7days in rat significantly decreased pilocarpine (4.0mg/kg, i.p.)-induced parotid salivary flow. Diazepam also produced a significant increase in the dissociation constant (Kd) value for [(3)H]dihydroalprenolol binding, but no change in the maximal binding capacity (Bmax) value, and a decrease in the Kd value for [(3)H]diazepam binding to benzodiazepine receptors, but no change in the Kd or Bmax values for [(3)H]prazosin or [(3)H]quinuclidinyl benzilate binding. These results suggest that continuous administration of diazepam modifies affinity for β-adrenoceptor and benzodiazepine receptor binding sites in parotid gland membrane and that changes in these binding sites may be closely related to diazepam-induced suppression of salivary secretion.

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.

Immunohistochemical study on GABAergic system in salivary glands

Gamma-aminobutyric acid (GABA) and its receptors are found in the central nervous system and several peripheral tissues. The purpose of this study was to determine the expression and distribution of GABA and glutamate decarboxylase (GAD), a GABA biosynthetic enzyme, in rat salivary gland. Western blot and real time quantitative RT-PCR revealed that GAD67 was the major isoform of GAD in the salivary glands. Furthermore, both GABA and GAD were detected around the acinar cells in the submandibular glands by immunohistochemical analysis. When both sympathetic and parasympathetic nerves related to the submandibular glands were denervated, the immunoreactivities of GABA and GAD were dramatically depressed, and levels of GAD67 and GABA significantly decreased. However, no morphological changes in the glands were observed after denervation. These results indicate that GAD67 is present around acinar cells in the salivary glands, and suggest that the GABAergic system in the glands is closely related to the autonomic nervous system.

Effect of translocator protein (18 kDa)-ligand binding on neurotransmitter-induced salivary secretion in rat submandibular glands

BACKGROUND INFORMATION

TSPO (translocator protein), previously known as PBR (peripheral-type benzodiazepine receptor), is a ubiquitous 18 kDa transmembrane protein that participates in diverse cell functions. High-affinity TSPO ligands are best known for their ability to stimulate cholesterol transport in organs synthesizing steroids and bile salts, although they modulate other physiological functions, including cell proliferation, apoptosis and calcium-dependent transepithelial ion secretion. In present study, we investigated the localization and function of TSPO in salivary glands.

RESULTS

Immunohistochemical analysis of TSPO in rat salivary glands revealed that TSPO and its endogenous ligand, DBI (diazepam-binding inhibitor), were present in duct and mucous acinar cells. TSPO was localized to the mitochondria of these cells, whereas DBI was cytosolic. As expected, mitochondrial membrane preparations, which were enriched in TSPO, exhibited a high affinity for the TSPO drug ligand, (3)H-labelled PK 11195, as shown by B(max) and K(d) values of 10.0+/-0.5 pmol/mg and 4.0+/-1.0 nM respectively. Intravenous perfusion of PK 11195 increased the salivary flow rate that was induced by muscarinic and alpha-adrenergic agonists, whereas it had no effect when administered alone. Addition of PK 11195 also increased the K(+), Na(+), Cl(-) and protein content of saliva, indicating that this ligand modulated secretion by acini and duct cells.

CONCLUSIONS

High-affinity ligand binding to mitochondrial TSPO modulates neurotransmitter-induced salivary secretion by duct and mucous acinar cells of rat submandibular glands.

Water channels and zymogen granules in salivary glands

Salivary secretion occurs in response to stimulation by neurotransmitters released from autonomic nerve endings. The molecular mechanisms underlying the secretion of water, a main component of saliva, from salivary glands are not known; the plasma membrane is a major barrier to water transport. A 28-kDa integral membrane protein, distributed in highly water-permeable tissues, was identified as a water channel protein, aquaporin (AQP). Thirteen AQPs (AQP0 - AQP12) have been identified in mammals. AQP5 is localized in lipid rafts under unstimulated conditions and translocates to the apical plasma membrane in rat parotid glands upon stimulation by muscarinic agonists. The importance of increases in intracellular calcium concentration [Ca(2+)](i) and the nitric oxide synthase and protein kinase G signaling pathway in the translocation of AQP5 is reviewed in section I. Signals generated by the activation of Ca(2+) mobilizing receptors simultaneously trigger and regulate exocytosis. Zymogen granule exocytosis occurs under the control of essential process, stimulus-secretion coupling, in salivary glands. Ca(2+) signaling is a principal signal in both protein and water secretion from salivary glands induced by cholinergic stimulation. On the other hand, the cyclic adenosine monophosphate (cAMP)/cAMP-dependent protein kinase system has a major role in zymogen granule exocytosis without significant increases in [Ca(2+)](i). In section II, the mechanisms underlying the control of salivary protein secretion and its dysfunction are reviewed.

Review: The physiology of saliva and transfer of drugs into saliva

Although saliva or oral fluid "lacks the drama of blood, the sincerity of sweat and the emotional appeal of tears", quoting Mandel in 1990 [I.D. Mandel, The diagnostic uses of saliva, J. Oral Pathol. Med. 19 (1990) 119-125], it is now meeting the demand for inexpensive, non-invasive and easy-to-use diagnostic aids for oral and systemic diseases, drug monitoring and detection of illicit use of drugs of abuse, including alcohol. As the salivary secretion is a reflex response controlled by both parasympathetic and sympathetic secretomotor nerves, it can be influenced by several stimuli. Moreover, patients taking medication which influences either the central nervous system or the peripheral nervous system, or medication which mimic the latter as a side effect, will have an altered salivary composition and salivary volume. Patients suffering from certain systemic diseases may present the same salivary alterations. The circadian rhythm determines both the volume of saliva that will and can be secreted and the salivary electrolyte concentrations. Dietary influences and the patient's age also have an impact on composition and volume of saliva. The latter implies a wide variation in composition both inter- and intra-individually. Sampling must therefore be performed under standardized conditions. The greatest advantage, when compared to blood sample collection, is that saliva is readily accessible and collectible. Consequently, it can be used in clinically difficult situations, such as in children, handicapped and anxious patients, where blood sampling could be a difficult act to perform.

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.