Preventive magnesium supplement protects the inner ear against noise-induced impairment of blood flow and oxygenation in the guinea pig.

We have recently demonstrated in the guinea pig that preventive dietary magnesium supplement can significantly reduce hearing loss caused by acute impulse noise exposure. To elucidate the underlying protective mechanisms of magnesium, the present study examined its effect on noise-induced impairment of cochlear blood flow (CoBF) and perilymphatic oxygen partial pressure (pO2) in two groups of guinea pigs maintained on optimal or suboptimal dietary magnesium status. While laser Doppler flowmetry was used to determine CoBF, perilymphatic pO2 was measured polarographically using micro-coaxial platinum needle electrodes. Auditory function was tested by recording compound action potentials. Animals were exposed to a selected high-intensity impulse noise series (L(peak) 167 dB, 1/s, 38 min). In the low magnesium groups, the noise exposure resulted in a mean decrease of CoBF and perilymphatic PO2 by about 10 and 35 per cent of the initial value, respectively. In contrast, in the high magnesium groups, neither parameter displayed any noise-induced decreases, and there was even a tendency to a slight increase. Magnesium also reduced the hearing loss significantly by 10 to 35 dB over the frequency range (2-16 kHz) tested. Both the CoBF and the perilymphatic pO2 were found to correlate with the serum magnesium. The piesent findings show that in the guinea pig preventive dietary magnesium supplement can protect the inner ear against noise-induced impairment of blood flow and oxygenation, which may partly be responsible for noise-induced hearing loss.