The protective effect of isoflurane and halothane on noise-induced hearing loss in mice

Abstract

Problem: Production of oxygen-free radicals and apoptosis are the mechanism of inner ear damage in noise-induced hearing loss. General anesthetics can inhibit the tissue metabolic activity, production of oxygen-free radicals, and apoptosis. We conducted this study to evaluate the protective effect of general anesthetics on hearing loss in noise-exposed mice. Methods: We used BALB/c mice with normal Preyer’s reflex. Mice were anesthetized with 1 - 1.5 MAC of isoflurane and halothane using end-tidal agent monitoring system with supplement of oxygen (4 L/min). Broad band white noise (120 dB SPL, 0.2 - 7 kHz) was used for induction of noise-induced hearing loss. Mice were stimulated by noise for 3 hours daily for 3 consecutive days with or without anesthetics (control). Hearing level was evaluated by measuring auditory brainstem response before and after noise exposure. Results: The hearing level before noise exposure was 26 ± 2 dB in the control group (n = 5). The level changed to 79 ± 1 dB after 3-day noise exposure and to 82 ± 1.5 dB 1 week after noise exposure. When we anesthetized the mice with isoflurane during noise exposure (n = 5), hearing levels were 22 ± 2.5 dB before noise exposure, 48 ± 6.5 dB after exposure and 29 ± 3.5 dB 1 week after noise exposure. In the halothane anesthetics group (n = 5), hearing levels were 20 ± 1.5 dB, 39 ± 2 dB, and 25 ± 3.5 dB, respectively. Conclusion: General anesthesia with isoflurane or halothane can protect the noise-induced hearing deterioration. Significance: The mechanism of this protective effect needs further studies. Support: None reported.