Human parotid responds in vitro to pentagastrin and melatonin

It is generally believed that salivary secretion is exclusively under nervous control. However, at variance with this prevailing view, our recent studies have shown some hormones to influence saliva composition. In rat parotid gland, melatonin, and gastrin-analogue pentagastrin, cause, by direct action, in vivo secretion of protein. In mammals, melatonin is secreted not only by the pineal gland but also by intestinal mucosal cells, and induces duodenal bicarbonate secretion. OBJECTIVES: Since studies are lacking with respect to an hormonal influence on the secretory activity of human glands, the present work aimed at evaluating morphological effects of melatonin and pentagastrin, in vitro, on human parotid glands. METHODS: Parotid samples, obtained at surgery from 40 subjects, were incubated in an oxygenated inorganic medium added with melatonin or pentagastrin. To quantify the effect of stimulation we investigated by high resolution scanning electron microscopy on osmium macerated tissues, the morphological changes in the intercellular canaliculi. RESULTS: To melatonin and pentagastrin, density of microvilli decreased (P<0.001, Mann-Whitney U-test) by 44% and 40%, respectively, while that of microbuds increased (P<0.001) by 45% and 280%, respectively (as compared to controls), whereas lumina were sparsely dilated. CONCLUSIONS: In analogy with our previous findings on human salivary tissues incubated with secretagogue muscarinic and adrenergic agonists mimicking nervous stimulation, we conclude that our present ultrastructural findings reflect secretory activity to pentagastrin and melatonin