Preventive magnesium supplement reduces ischemia-induced hearing loss and blood viscosity in the guinea pig

The effect of magnesium (Mg) on ischemia-induced hearing loss was investiga ted in two groups of adult pigmented guinea pigs of either an optimal or su boptimal (physiologically high or low) Mg status maintained by different di ets. Total Mg concentrations of the perilymph, cerebrospinal fluid, blood p lasma and red blood cells were found to differ significantly between the tw o groups, as tested in a previous study. Local vascular impairment was prod uced by unilateral ferromagnetic thrombosis of cochlear blood vessels. Coch lear blood flow (CBF) and hearing function were measured using laser Dopple r flowmetry and auditory brain-stem response audiometry, respectively. Ferr omagnetic thrombosis resulted in significant reductions of the mean apical CBF in both experimental groups and of the mean basal CBF in the low Mg gro up compared to the contralateral ears. In the high Mg group, the basal CBF was not decreased. However, the laser Doppler signals revealed considerable interindividual variations and the differences found between the two exper imental groups were not significant. In contrast, the hearing loss in the l ow Mg group was significantly higher than that in the high Mg group. A corr elation was found to exist between the vascular impairment and the hearing threshold shift. In a separate series, we also tested the effect of Mg on h emorheology and found both the blood viscosity and blood viscoelasticity to be significantly lower in the high Mg group than in the low Mg group, depe nding on the shear rates tested. The present findings show that a preventiv e oral Mg supplement can significantly reduce the rate of ischemia-induced hearing loss and improve blood viscosity in the guinea pig.