The effect of external fractionated irradiation on the distribution pattern of extracellular matrix proteins in submandibular salivary glands of the rat

INTRODUCTION: The aim of this study was to analyse the distribution pattern of extracellular matrix proteins in the irradiated and non-irradiated rat submandibular salivary gland in order to provide a more detailed profile of the radiation injury following radiotherapy of the head and neck.

MATERIAL AND METHODS: External X-ray exposure, restricted to the left skull base and neck region, was performed in 60 female Wistar rats, fractionated to daily applications of 2 Gy, up to total dosages of 20, 40 or 60 Gy. Both submandibular glands were excised after supravital anaesthesia 6 months or 1 year after completion of the irradiation. Spatial and temporal patterns of extracellular matrix proteins were investigated histologically and immunohistochemically.

RESULTS: The polyclonal anti-human antisera used, identified the same antigens in rat tissue as in human tissues. The alterations in staining patterns and staining intensities between irradiated and non-irradiated salivary glands showed statistically significant differences. Different structures in irradiated glands reacted with different intensities, e.g. nerve tissue and the basement membranes of excretory ducts were intensely laminin-positive, fibronectin was predominantly found around the excretory ducts with transition to the interstitial tissues.

CONCLUSION: Irradiation leads to statistically significant differences in the amount and composition of the extracellular matrix in salivary glands. The amount of extracellular matrix proteins in irradiated glands is dose-dependent. The higher the dosage the more extracellular matrix can be expected. Consecutively, total dosage is associated with greater loss of acini. Scatter effects of irradiation have also to be recognized. Immunohistochemical studies on salivary glands have to consider the pretreatment status, in particular those studies that investigate degenerative changes.