[An electron microscopic study of thyroxine against ototoxicity of kanamycin]

Forty-five guinea pigs were randomly divided into 2 groups: 15 in the control group and 30 in the experimental group. All animals were injected immediately with 400 mg/kg kanamycin for 10 days. At the same time, the experimental animals were given orally 10 mg/kg thyroxin every other day 5 times. All animals were decapitated 10 days after administration of drugs and measurement of ABR. Then, the specimens of cochlea were prepared for both SEM and TEM. The result of SEM showed that the degeneration and loss of stereocilium in each turn was significantly milder in the experimental group than in the control. Under TEM, outer and inner hair cells showed changes caused by kanamycin. In the experimental group, the mitochondrias were basically normal. The secondary lysosomes gathered under cuticular plate and supranuclear area. In the control group, the mitochondria showed pyknosis and high density, and multivesicular bodies were increased. The cytoplasm was swelling. There were many vacuoles produced by accumulation of liquid in the cytoplasm. Based on the findings of ultrastructural changes of cochlear hair cells, the mechanism of thyroxine against ototoxicity of kanamycin was discussed.