THE EFFECT OF HYPOGLYCEMIA ON COCHLEAR MICROPHONICS

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With the purpose to clarify the relationship between sugar metabolism and inner ear function, the author investigated the effect of insulin on cochlearmicrophonics as well as the behavior of blood circulation and glycogen precipitation in the inner ear. Cochlear microphonics and action potentials were measured by means of vestibulotympanal recording in guinea-pigs and round window recording in cats, using pure tone and click sound. In order to know the condition of the blood flow in the inner ear, continuous registration of the veiocity of the blood and the pressure in the vertebral artery, internal carotid artery and internal jugular vein were obtained using Rein's The rmostromuhr. The venous blood sugar level was estimated by Somogyi's micro-colorimetric method.The intravenous injection of regular insulin caused the decrease of blood sugar level, hypotension and lowering of the body temperature. On the other hand, the blood flow in the vertebral artery increased promoting the circulation in the inner ear. The hypoglycemic condition induced by insulin injection did not depress the sensitivity of cochlear microphonics, as far as the heart was in normal function, even in the hypophysectomyzed guinea-pig. The recovery time of cochlear microphonics was not affected after the exposure to pure tone of 95 phon at 4000cps for 30 seconds, while a remarkable delay was shown after the transient cessation of breathing in the hypoglycemic animals. Determined by PAS reaction with salivary digestion, the precipitation of glycogen in the inner ear tissue was not modified by insulin injection, except in the hypophysectomyzed guinea-pig.In the condition of insulin hypoglycemia, the function of the inner ear was well preserved to be compensated by the increase of the blood flow in the vertebral artery. In the case of the lack of oxygen supply, however, the sugar metabolism was disturbed and the sugar reserved in the tissue was utilized. When the reserved sugar was used up, the function of the inner ear was disturbed by the hypoglycemia. The blood sugar was believed to be an indispensable factor in the maintenance of the inner ear function.