Low-frequency noise effects on the parotid gland of the Wistar rat

Background: Long-term low-frequency noise (LFN) (≤500 Hz) exposure is known to cause extracellular matrix proliferation by fibrosis in the absence of inflammatory signs. Aim: We have examined the morphofunctional alterations of the parotid glands of Wistar rats exposed to LFN. The hypothesis is that the parotid glands are a target for LFN-induced lesions. Materials and methods: Ten rats were exposed to LFN for 2184 consecutive hours while 10 rats were kept under similar conditions but in silence for control purposes. The parotid glands were surgically removed. One gland was sectioned and stained with hematoxylin-eosin and periodic acid Schiff for light microscopy observation. The other was used for functional amylase secretion measurements, basal and nerve-mediated [with electrical field stimulation (EFS)] and secretagogue-evoked secretion [acetylcholine (ACh) 10^-5 M] with established fluorimetric techniques. Results: All the rats exposed to LFN showed marked morphological lesions including vacuolar degeneration, hyalinization, cell death and blood vessels wall focal thickening. No morphological changes were detected in the control group. The functional results presented significantly diminished basal, EFS and ACh-evoked amylase secretion when compared with the control group. Conclusion: These results suggest that the parotid gland is a target for LFN-induced lesions with an impairment of its function.