Inhibition of pilocarpine-induced saliva secretion by adrenergic agonists in ICR mice

Abstract

The aim of the present study was to clarify the effects of the adrenoceptor agonist isoproterenol (IPR) on saliva secretion stimulated by the muscarinic receptor agonist pilocarpine (PILO) in mice. Mice were injected with either 0.5 mg/kg, i.p. PILO alone or simultaneously with 2 mg/kg, i.p., IPR to evaluate the inhibitory effects of adrenoceptor agonists on saliva secretion. The mechanisms underlying changes in saliva flow rate were evaluated by histological examination of aquaporin 5 (AQP5) and saliva flow rate using the adenylate cyclase (AC) inhibitor SQ22536 (0.25 mg per mouse, s.c.), which was administered 30 min prior to PILO and/or IPR. Saliva volume decreased significantly in the mice treated simultaneously with PILO + IPR compared with that in mice treated with PILO alone. Changes in the intracellular localization of AQP5 were seen in PILO + IPR-treated mice, and those changes were reversed by SQ22536 pretreatment. In addition, the decreased salivary flow rate in the PILO + IPR-treated mice was partially restored by SQ22536 pretreatment. There were no significant changes in intracellular calcium or ATP levels among the groups. The results of the present study suggest the existence of an inhibitory effect of the sympathetic nervous system on parasympathetic-stimulated salivary secretion from the salivary gland.

Keywords: aquaporin 5; autonomic nerve; isoproterenol; pilocarpine; saliva; stress.