Pentagastrin-induced nitric oxide-dependent protein secretion from the parotid gland of the anaesthetized rat

World Workshop on Oral Medicine VI: a systematic review of medication-induced salivary gland dysfunction

The aim of this paper was to perform a systematic review of the pathogenesis of medication-induced salivary gland dysfunction (MISGD). Review of the identified papers was based on the standards regarding the methodology for systematic reviews set forth by the World Workshop on Oral Medicine IV and the PRISMA statement. Eligible papers were assessed for both the degree and strength of relevance to the pathogenesis of MISGD as well as on the appropriateness of the study design and sample size. A total of 99 papers were retained for the final analysis. MISGD in human studies was generally reported as xerostomia (the sensation of oral dryness) without measurements of salivary secretion rate. Medications may act on the central nervous system (CNS) and/or at the neuroglandular junction on muscarinic, α-and β-adrenergic receptors and certain peptidergic receptors. The types of medications that were most commonly implicated for inducing salivary gland dysfunction were those acting on the nervous, cardiovascular, genitourinary, musculoskeletal, respiratory, and alimentary systems. Although many medications may affect the salivary flow rate and composition, most of the studies considered only xerostomia. Thus, further human studies are necessary to improve our understanding of the association between MISGD and the underlying pathophysiology.

Reduced muscarinic parotid secretion is underlain by impaired NO signaling in diabetic rabbits

OBJECTIVES

The influence of experimental diabetes (alloxan, 100 mg kg(-1) ) was studied on rabbit parotid gland function.

MATERIAL AND METHODS

Carbachol-induced parotid secretion in vivo, and in vitro quantification of inducible nitric oxide synthase (iNOS) mRNA expression, by real-time RT-PCR, and activity of superoxide dismutase (SOD) and total antioxidant capacity (TAC) in commercial colorimetric assays were measured in parotid glands of non-diabetic and diabetic rabbits.

RESULTS

Carbachol-induced dose-dependent increase in parotid secretion significantly reduced in diabetic rabbits. Functional studies in the presence of muscarinic receptor and nitric oxide synthase (NOS) antagonists revealed that in M3 receptor-mediated carbachol secretion, nitric oxide, deriving mainly from neuronal NOS (nNOS) in control, and iNOS in diabetic rabbits, was involved. Also, upregulation of iNOS mRNA expression and enhanced SOD activity and TAC were detected in diabetic glands.

CONCLUSIONS

Our data suggest that decreased M3 receptor-mediated parotid secretion in diabetic rabbits appears to be due to alterations in NO signaling, mainly due to iNOS induction, accompanied by elevated antioxidant response.

Morphological evidence that pentagastrin regulates secretion in the human parotid gland

Salivary secretion is principally regulated by autonomic nerves. However, recent evidence from in vivo animal experiments suggests that gastrointestinal peptide hormones can also influence saliva production. The aim of the present study was to define the secretagogue activity of the gastrin-analogue pentagastrin in human salivary glands. For this purpose, parotid tissues were exposed to pentagastrin in vitro. Morphological techniques were used to evaluate modifications to serous acinar cells associated with secretion. Using a variant of the osmium maceration method, high resolution scanning electron microscopy allowed assessment of the morphology of the cytoplasmic aspect of the plasmalemma to demonstrate secretory activity. To quantify responses to pentagastrin, we recorded morphometric data on microvilli, microbuds, and protrusions. Dose-dependent morphological changes were observed, whereas protein concentration increased in the incubate. The use of selective receptor antagonists showed pentagastrin to act principally via cholecystokinin-A receptors. The morphological responses observed following exposure to pentagastrin differed from those elicited following exposure to the pan-muscarinic agonist carbachol. This study provides the first demonstration of a direct secretory action of gastrointestinal peptides on salivary glands in humans.

Anti-inflammatory action of cholecystokinin and melatonin in the rat parotid gland

OBJECTIVE

To define the influence of cholecystokinin and melatonin on the inflammatory response of the lipopolysaccharide-exposed rat parotid gland.

MATERIALS AND METHODS

Bacterial lipopolysaccharide was infused retrogradely into the parotid duct. The degree of inflammation three hours postadministration was estimated from the activity of myeloperoxidase, reflecting glandular neutrophil infiltration.

RESULTS

The myeloperoxidase activity of the lipopolysaccharide-exposed gland was 10-fold greater than that of the contralateral gland. Combined with sulphated cholecystokinin-8 (10 or 25 μg kg(-1) , given twice intraperitoneally) or melatonin (10 or 25 mg kg(-1) x 2) the lipopolysaccharide-induced response was elevated 4.6- and 3.5-folds at the most. The cholecystokinin-A receptor antagonist lorglumide reduced the inhibitory effect of cholecystokinin-8, while the melatonin 2-preferring receptor antagonist luzindole had no effect on the melatonin-induced inhibition. Unselective nitric oxide-synthase inhibition abolished the increase in myeloperoxidase activity, whereas inhibition of inducible or neuronal nitric oxide-synthase (of non-nervous origin) halved the inflammatory response.

CONCLUSION

Some hormones may contribute to anti-inflammatory action in salivary glands in physiological conditions. They are potential pharmacological tools for treating gland inflammation. The inflammation, as judged from the myeloperoxidase activity, was entirely dependent on nitric oxide-synthase activity, indicating that the hormones directly or indirectly reduced the generation of nitric oxide.

The influence of estrogen and progesterone on parasympathetic vasodilatation in the rat submandibular gland

Previous studies suggest that NO- and PGI(2)-independent pathways play a greater role in parasympathetic vasodilatation in the submandibular glands (SMG) of female than of male rats. Thus, the purpose of this study was to determine whether estrogen and progesterone influence the relative contributions of NO and PGI(2) to parasympathetic vasodilatation in the SMG. Vascular responses to chorda-lingual nerve stimulation were examined in sham-operated (SHAM) and ovariectomized (OVX) female rats and in OVX rats treated with either 17beta-estradiol alone or a combination of 17beta-estradiol and progesterone. Compared with SHAM animals, increases in vascular conductance in OVX rats were reduced at 1, 2 and 5 Hz (p<0.05). Blood flow responses in OVX+17beta-estradiol and OVX+17beta-estradiol+progesterone rats were indistinguishable from those observed in SHAM animals. Indomethacin had no effect on vasodilatation in SHAM and OVX+17beta-estradiol rats, but increased vascular responses in OVX animals (p<0.02). The addition of L-NAME resulted in a significant reduction in vasodilatation at all frequencies. In OVX rats treated with both estrogen and progesterone, indomethacin caused a reduction in vasodilatation and L-NAME further diminished the remaining responses. Under all conditions, vasodilatation was due largely, if not exclusively, to direct parasympathetic rather than antidromic sensory nerve activation. Finally, both neuronally-derived and endothelium-derived NO appeared to be responsible for the NO-dependent vasodilatation, but endothelium-derived NO became increasingly important as the frequency of stimulation increased. We conclude that estrogen and progesterone influence parasympathetic vasodilatation through combined effects on NO-, PGI(2)- and non-NO/PGI(2)-mediated pathways.

Melatonin-evoked in vivo secretion of protein and amylase from the parotid gland of the anaesthetised rat

The intravenous infusion of melatonin (5 and 25 mg/kg over 10 min) evoked a dose-dependent output of protein and amylase but no overt fluid secretion from the parotid gland of the pentobarbitone-anaesthetised rat, as revealed by increased concentrations of protein and amylase activity in a subsequent wash-out flow of saliva in response to an intravenous bolus injection of methacholine (5 microg/kg) 10 min later. The secretory responses to melatonin occurred in the presence of alpha- and beta-adrenoceptor antagonists. They were not affected by the cholecystokinin A-receptor antagonist, lorglumide, and they were reproduced in eviscerated animals acutely subjected to postganglionic sympathetic and parasympathetic denervation of the gland. The responses to melatonin were partially dependent on nitric oxide generation, through the activity of nitric oxide synthase of the neuronal type. Immunoblotting showed both melatonin receptors of type 1 and type 2 to be expressed in parotid gland tissue. The relative specific melatonin 2-receptor antagonist luzindole prevented the expected secretory effects of melatonin. The results favour a direct action by melatonin on melatonin receptors of parotid secretory cells and suggest a potential physiological role for melatonin in the regulation of salivary glandular activities.