Preventive effect of magnesium supplement on noise-induced hearing loss inthe guinea pig

The effect of magnesium (Mg) on noise-induced hearing loss was investigated in two groups of adult pigmented guinea pigs maintained either on optimal or suboptimal (physiologically high or low) Mg produced by different diets. The total Mg concentrations of the perilymph (PL), cerebrospinal fluid, bl ood plasma and red blood cells were measured by atomic absorption spectrome try and were found to differ significantly between the two groups (P < 0.01 ). One ear of each animal was exposed to either a single shooting impulse a t a peak pressure level of 187 dB or two impulse noise series at a rate of 1/s and peak pressure levels of 150 dB (1,000 impulses) and 167 dB (2,280 i mpulses), respectively. Temporary (TTS) and permanent (PTS) hearing thresho ld shifts in anesthetized animals were measured 2 h and 1 week after the no ise exposure, using auditory brain stem response (ABR) audiometry at a freq uency range from 3.75 to 30 kHz. Exposure to the single noise impulse resul ted in a mean TTS that was significantly lower in the high ME group than th at in the low Mg group (P < 0.05), although no substantial PTS was observed in either group. In the animals exposed to 150 dB noise, the TTS showed a tendency towards an Mg-related reduction at the higher frequencies. A small difference in PTS was found between the low Mg and high Mg groups, but was not significant. Exposure to the 167-dB noise series caused a considerable TTS, which was significantly lower in the high Mg group at 7.5 and 15 kHz than in the low Mg group (P < 0.05). The mean PTS showed a significant diff erence between the two Mg groups over the whole frequency range (P < 0.05) and was found to correlate negatively with the total Mg concentrations of b oth PL and plasma (P < 0.05). Moreover, the high Mg group showed a faster r ecovery from the hearing threshold shift than the low Mg group. The present findings show that preventive oral Mg supplements can significantly reduce the rate of acoustic trauma caused by high-level impulse noise exposure in the guinea pig.