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

Abstract

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.

Expression and cellular localizaion of melatonin-synthesizing enzymes in rat and human salivary glands

“…In addition, immunohistochemical analysis for Mel1aR revealed that Mel1aR was not expressed in any cells in submandibular glands (data not shown). This finding is inconsistent with the previous report that melatonin evoked protein secretion in rat parotid glands (CevikAras and Ekström 2010; Aras and Ekström 2008). Other receptors such as melatonin receptor 1b may be expressed and regulate protein secretion in parotid glands.…”

Subcellular distribution of melatonin receptors in human parotid glands

“…In humans, using light microscopy, the presence of MT1-receptor immunoreactivity was reported in parotid glands (Aneiros-Fernandez et al 2012;Arias-Santiago et al 2012) but not in submandibular glands (Shimozuma et al 2011). Both MT1 and MT2 receptors have been demonstrated by immunoblotting in rat parotid glands (Cevik Aras & Ekstr€ om, 2008). The MT2 type mediates protein synthesis, as well as the secretion of protein/ amylase (Cevik Aras & Ekstr€ om, 2008;Cevik-Aras et al 2011).…”

“…Most of the biological functions of melatonin are thought to be mediated by the membrane receptors, melatonin 1 (MT1) and 2 (MT2). In addition to their presence in the central nervous system, melatonin receptors are found in several peripheral structures, such as duodenal enterocytes (Sj€ oblom & Flemstr€ om, 2003Slominski et al 2012), gall-bladder epithelium (Aust et al 2004), the exocrine pancreas (Aust et al 2008), the endocrine pancreas (Mulder et al 2009), the skin (Slominski et al 2005(Slominski et al , 2012 and the parotid gland (Cevik Aras & Ekstr€ om, 2008). In humans, using light microscopy, the presence of MT1-receptor immunoreactivity was reported in parotid glands (Aneiros-Fernandez et al 2012;Arias-Santiago et al 2012) but not in submandibular glands (Shimozuma et al 2011).…”

“…Both MT1 and MT2 receptors have been demonstrated by immunoblotting in rat parotid glands (Cevik Aras & Ekstr€ om, 2008). The MT2 type mediates protein synthesis, as well as the secretion of protein/ amylase (Cevik Aras & Ekstr€ om, 2008;Cevik-Aras et al 2011). Interestingly, melatonin was shown to induce in vitro ultrastructural changes in a preliminary report, indicating secretory activity, in pieces of human parotid gland (Loy et al 2010).…”

Melatonin: A Novel Indolamine in Oral Health and Disease

“…Melatonin is a novel oesophageal protector acting through COX/Prostaglandin and NOS/NO systems and via activation of sensory nerves [60]. Novel evidence implicates that melatonin may have potential to treat xerostomia by evoking protein/amylase secretion from the parotid gland of anaesthetised rats [61]. In hamsters, the quantity of melatonin consumed in foodstuffs may influence caries incidence [36].…”