VITAMIN-A-DEFICIENCY INCREASES NOISE SUSCEPTIBILITY IN GUINEA-PIGS

The effect of vitamin A deficiency in guinea pig on noise-induced temporary threshold shift (TTS) was evaluated after short (15 min) acoustic overstimulation with a moderate (90 dB) broad-band white noise. Some guinea pigs were fed ad libitum a purified diet deficient in vitamin A (VAD group) until biochemical signs of deficiency occurred. A second, control group (VA group) received the same diet as well as 100 IU vitamin A daily by pharyngeal tube. Cochlear potentials were recorded by special computerized equipment using implanted electrodes. Before acoustic stimulation, a baseline value was determined with a test stimulus [90 dBA (A-filter according to usual DIN instructions)] corresponding to that for TTS measurements. Noise-induced changes were determined by calculating the changes in latency and amplitude of the N1-signal of the compound action potential (CAP) at various times (1, 3, 5, 7, 11 min) after termination of acoustic stimulation in comparison with baseline values. Statistical analysis of the CAP data showed that the VAD group had significantly smaller amplitudes and increased latency of the N1-potential after acoustic stimulation and that the VA group did not show a significant change in amplitude or latency. The reduction in N1-amplitude and N1-latency in the VAD group reflects changes in inner ear hair cell activity. We conclude that vitamin A deficiency increases the sensitivity of the inner ear to noise and that this increased sensitivity increases the probability of noise-induced hearing loss.