Mechanism of salivary secretion enhancement by Byakkokaninjinto

Byakkokaninjinto (BN) is a Kampo preparation used for the treatment of xerostomia induced by drug, ageing, Sjogren syndrome, etc. The mechanism for BN to induce salivary secretion has not been made clear. In this study, various rat thirst models were prepared using muscarinic receptor blockers, such as 4-diphenylacetoxy-N-methylpiperidine (4-DAMP) and atropine, or adrenoceptor blockers, such as phentolamine and propranolol, in order to investigate the efficiency of BN. When BN was orally administered to the rats in the dose range of 100 to 300 mg/kg, the salivary secretion increased in a dose-dependent manner. The suppression of salivary secretion induced by phentolamine, atropine, and 4-DAMP was recovered by the additional treatment of BN. Interestingly, BN treatment increased the expression of aquaporin 5 in rats, which is known to regulate salivary secretion from the submandibular gland. These results suggested that BN increased the expression of aquaporin 5 through activation of muscarinic M3 receptor and enhanced salivary secretion.