Inhibition of parasympathetic saliva flow by sympathetic nerve stimulation

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Both sympathetic and parasympathetic nerve stimulate saliva secretion in the salivary gland, and both of them have not been thought to have mutual antagonism. The purpose of the study is to study the interaction between sympathetic and parasympathetic nerve in the mouse salivary gland.When pilocarpine (a muscarinic receptor agonist) and isoproterenol (β-adrenoceptor agonist) were given mouse at the same time, quantity of saliva flow significantly decreased compared to pilocarpine single administration. Immunohistochemistory showed that the labeling of aquaporin 5 (AQP5) was localized in the plasma membrane of the submandibular and parotid glands when the mouse was stimulated by pilocarpine. When pilocarpine and isoproterenol were administered at the same time, strong and diffuse labeling AQP5 was seen in the cytoplasm, and difference of the staining intensity between the plasma membrane and cytoplasm became small compared to the single administration of pilocarpine. When SQ22536 which inhibited adenyl cyclase was administered before administering pilocarpine and isoproterenol, the changes of the AQP5 localization was restored, and as a result decrease of salivation was restored partially. The results presented here suggest that isoproterenol suppress the pilocarpine-stimulated salivary flow via AC cAMP-PKA axis. Changes of AQP5 localization stimulated by isoproterenol possibly contributed as a mechanism in the suppression of saliva flow.In conclusion, sympathetic nerve stimulation inhibited parasympathetic nerve system in salivary gland tissue, which was demonstrated by the in vivo experiment.