Secretion of saliva in X-irradiated rat submandibular glands.

The mechanism of radiation-induced dysfunction in rat submandibular glands was investigated at the cellular level. After X irradiation (single dose, 15 Gy), a vacuolation in the acinar cells or an enlargement of the acinar lumen was observed as a typical morphological change for 2 weeks. As observed using a video-enhanced contrast differential interference contrast (VEC-DIC) microscope, exocytosis and shrinkage of the acinar cells induced by application of pilocarpine (100 microM) were markedly suppressed for 5 days and then recovered to 80% of the control levels. Using an immunohistochemical method, no significant change was observed in amylase distribution, but a marked loss of aquaporin 5 was found in the acinar cells after the irradiation. The extent and time course of pilocarpine-induced mobilization of intracellular Ca(2+) did not change after the irradiation. We conclude that radiation-induced dysfunction in the salivary glands is due to an impairment of exocytosis and a reduction of water secretion. The loss of aquaporin 5 and possibly other membrane-fusion proteins in acinar cells may be the major mechanism underlying such a dysfunction.