Electrocochleographic Changes Induced by Glycerol Administration in Hydropic Guinea Pigs

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Glycerol is known to improve hearing acuity in Meniere's disease. Experimentally induced endolymphatic hydrops in guinea pigs was used as a model of Meniere's disease, and the effect of glycerol on the cochlear potentials was measured.In 7 albino guinea pigs the endolymphatic sac of one ear was obliterated surgically to produce endolymphatic hydrops. In the 6th postoperative month, glycerol (50 % W/V, 6 ml/kg BW) was injected intravenously, and the electrocochleogram was recorded before, and 1 and 2 hours after the injection. Glycerol did not improve the thresholds of the cochlear microphonics (CM) and compound action potentials (AP). The same dose of glycerol was administered to 5 normal guinea pigs. The elevation in AP threshold for the click and the diminution in the AP amplitude for the click and the tone bursts of the middle and high frequencies were slightly greater in the hydropic ears than in the normal ears. Glycerol caused almost no change in CM thresholds and made the CM amplitudes slightly smaller for the tone bursts of the low and middle frequencies in both of the hydrops and control groups. These findings were contrary to the improvement of hearing in patients treated with glycerol. Furthermore, the amplitudes of +SP for the click were decreased at 1 hour in 4 animals and recovered by 2 hours after the injection in 2 of the 4. This finding was also quite different from that reported in papers describing the diminution of -SP in patients with Meeniere's disease.