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The influence of noise exposure on the endothelial transport system in the cochlea was investigated using cationic polyethyleneimine (PEI), since systemically administered PEI passes through the capillary endothelial cell and attaches to basal lamina (BL) anionic sites in the cochlea. Under general anesthesia, all guinea pigs were administered an intravenous injection of 0.5% PEI. Thirty minutes later, five animals were exposed to noise (10 kHz, broad band noise, 105 dB SPL) for 30 min, via speakers inserted into the external auditory canal. The remaining five animals (controls) were left without noise exposure for 1 h following PEI injection. All guinea pigs were then immediately sacrificed, and the bony labyrinths were removed. PEI distribution on the BL was assessed in the stria vascularis, spiral ligament, basilar membrane, spiral limbus and Reissner’s membrane throughout the cochlea with transmission electron microscopy. Compared to control animals, PEI distribution in the noise-exposed animals was significantly increased in the strial vessels of the basal and second turns and in Reissner’s membrane of all turns. In the spiral ligament, basilar membrane and spiral limbus, no significant difference in PEI distribution was observed between the control and noise-exposed animals. These findings indicate that noise exposure increases macromolecular transport in the stria vascularis but not in the spiral ligament, spiral limbus and basilar membrane and that systemically administered macromolecules are more readily transported to Reissner’s membrane by noise exposure. [ABSTRACT FROM AUTHOR]