Aquaporin 5 (AQP5) plays an important role for the transcellular fluid secretion in salivary gland cells. In this study, we compared acetylcholine (ACh)-induced salivary secretion and blood flow (BF) dynamics in submandibular gland (SMG) in rat strain with low levels of AQP5 protein (AQP5/low), Sprague-Dawley (SD) and Wistar/ST rats.The whole saliva secretion with high-dose of ACh (720~1440 nmol/min) in AQP5/low and Wistar/ST were~70% of that in SD. The level of AQP5 protein in Wistar/ST was same as that in AQP5/low, and was much lower than that in SD, suggesting that the AQP5 level determine the maximum rate of salivary secretions.Interestingly, the salivary secretions with low-dose of ACh (60~120 nmol/min) in Wistar/ST was two times higher than that of AQP5/low, and was comparable to that in SD. The ED₅₀ values for ACh-induced salivary secretion in AQP5/low, Wistar/ST, and SD were 309, 102, and 134 nmol/min, respectively. These results suggest that ACh sensitivity in salivary secretion does not correlate with AQP5 levels. Monitoring of BF in SMG demonstrated that low-dose of ACh induced oscillatory changes in BF in all strains. The BF oscillations in Wistar/ST wereobservedmostlyabove the resting level, whereas that in AQP5/low were observed below the resting level. We also found that angiotensin II-mediated vasoconstriction reduced BF during ACh stimulations, resulting in a decrease insalivary secretionin AQP5/low.These results suggest that the regulation of salivary secretionwith physiological stimuli can be determined by BF rather than by the level of AQP5.