Mechanism of heat acclimation-induced improvement of salivary secretion in rats

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We investigated mechanism of heat exposure-induced improvement of salivary function in rats. Two-day heat exposure increased expressions of aquaporin (AQP)1 and 5 mRNA in submandibular glands of rats concomitant with the promotion of the HIF-1a pathway, leading to VEGF induction. The protein level of AQP1 was raised after 2 or 5 day-heat exposure. The apical membrane distribution of AQP5 in serous acinar cells enhanced after heat acclimation, while AQP1 expression was restricted to the endothelial cells in the submandibular glands. Spontaneous exercise for 40 days tended to elevate AQP1 protein level of the rat submandibular glands, whereas it failed to affect AQP5 expression and protein levels of TRPV1, V3 or Na-K ATPase, relating to induce AQP5. Pilocarpine-induced salibary secretion was slightly elevated. These results suggest that in rats, heat exposure or exercise facilitates AQP expression in salivary glands, which may then contribute to improving saliva gland function.