The Study On Secretory Hypofunction Of Paracellular Pathway In Rat Submandibular Glands Resulted From Ionizing Radiation

Objective: To investigate the effects on the secretory function of paracellular pathway in rat submandibular glands(SMGs)caused by ionizing radiation and reveal the changes of tight junction(TJ)protein claudin-4.Methods: Twenty-four Wistar rats were randomly divided into control group and irradiation groups.The experimental SMGs of the irradiation groups were exposed to X-radiation at a single dose of 20 Gy.At 1,4,and12 weeks after irradiation,the resting salivary flow of SMGs was detected by Schirmer’s experiment.The changes of the gland tissues in pathology after hematoxylin-eosin(HE)staining were examined by light microscope.The TJ structures were detected by transmission electron microscope.Immunofluorescence staining,real time fluorescence quantitative polymerase chain reaction(RT-q PCR),and western blot analyses were used to detect the expression levels of muscarinic acetylcholine M3 receptor,aquaporin 5(AQP5),and claudin-4 protein.Results: At 1,4,and 12 weeks after irradiation,the secretion of SMGs was significantly decreased and much lower than that in control group(P <0.01).At 1 week,interstitial edema was mainly observed in SMG tissues.Moreover,nuclear pyknosis,decreased number of acinar cells,and small focal necrosis with inflammatory infiltration were also observed over time.However,these changes were most obvious at 12 weeks post-irradiation.In irradiation groups,the TJ ultrastructure of the glands at different times appeared to be fuzzy,collapsed,and decreased electron density.Moreover,the width of TJs was remarkably decreased(P < 0.01).The expression levels of M3 and AQP5 were decreased in time-dependent and the fluorescence intensity was significantly reduced after irradiation.However,the expression levels and fluorescence intensity of claudin-4 were enhanced in different degrees.Conclusion: The changes of TJ structure,the up-regulation of claudin-4 expression,and the damage of paracellular pathway were involved in the secretory hypofunction of the submandibular glands after irradiation.