Abstract
FOK rats are resistant to heat-exposure and cold-exposure, and great amount of salivation is found under the condition of heat-exposure (HE). To investigate how the enhanced salivation in FOK rats is related to the resistance to HE, we investigate immunohistochemical expression of aquaporin5 (AQP5) in submandibular gland in FOK rats and WKAH rats. AQP5 was detected in apical membrane (AM) and lateral membrane (LM) of acinar cells in both strains, although AQP5 expression was also found in basal membrane (BM) in FOK rats. Although expression pattern of AQP5 did not changed in both strains under HE (40°C), immunoreactivity to AQP5 was significantly decreased in WKAH rats. However, it did not changed in FOK rats. Blockage of parasympathetic effect by atropine (1 mg/kg) under HE caused inhibition of salivation, while decrease of AQP5 was found in not acinar cells but granular duct in FOK rats. On the other hand, injection of parasympathetic agonist policarpine (1mg/kg) induced salivation in both strains. Localization of AQP5 after pilocarpine injection was similar to that of HE. Expression of AQP5 in acinar cells was significantly only in WKAH rats. However, decrease of AQP5 expression in granular cells was found in both strains, and it was stronger in FOK rats. Data suggest that mechanism of enhanced salivation under HE is different from that by pilocarpine injection in FOK rats. [Jpn J Physiol 55 Suppl:S85 (2005)]
