[Respiratory epithelia in Wistar rats after 48 hours of continuous exposure to low frequency noise]

Previous studies show that exposure to low frequency noise (LFN) (< or =500 Hz, including infrasound) produces irreversible lesions in Wistar rat respiratory epithelia. Recovery periods for LFN-induced lesions have thus become an object of interest. Changes in the respiratory epithelia of Wistar rats after continuous short-term exposure to LFN are described. Twelve rats were exposed to continuous LFN for 48 hrs, and 10 age-matched rats were kept in silence. Animals were treated in accordance with 86/609/CE. After exposure ceased, two rodents were sacrificed immediately, and another two after 6, 12, 24, 48 hrs, and 7 days of post-exposure silence. Respiratory epithelial fragments were prepared for light and scanning/transmission electron microscopy. Six hours after exposure, intense and irregular cellular tumefaction was visible and rosetta structures, formed by secretory cells (SC) centered on a brush cell (BC), were identifiable. Cilia were shorter and shaggy. BC microvilli tended to group, losing the uniform distribution seen in controls. Twelve hours after exposure, cell ballooning was still present, BC shape was highly irregular and microvilli were grouped. SC microvilli were still shorter than controls. Seven days after exposure, controls and exposed were indistinguishable. LFN-induced epithelial lesions seem to be reversible if recovery periods are respected.