Although sensory neural hearing loss stemming from hypercholesterolemia has received attention in recent years, no information is available abut inner ear injuries resulting from this condition. In this study, we prepared guinea pig models at hypercholesterolemia and observed the inner ear with a transmission electron microscope, and also investigated the effect of vitamin E (Vit. E) on these injuries. One hundred and thirty-nine white male Hartley guinea pigs weighing a mean of 250 g each were divided into three groups. Group A consisted of the control animals, which were fed by a stock diet. Group B animals were fed by a hyperlipid diet (2.5% cholestrol, 0.25% cholic acid, and 7.5% cattle fat). Group C animals were fed by a Vit. E-added (50 units/100 g) hyperlipid diet. All the animals were sacrificed either one, two or three months after treatment and the cochlea duct vasculature, cochleal nerve fiber under spiral limbus, stria vascularis and inner hair cell and outer hair cell of Corti's organ was observed with a transmission electron microscope. Cholesterol, triglyceride, and TBARS values were concurrently measured in the serum. Auditory threshold was measured by auditory brain stem response (ABR).
In groups B and C, cholesterol and trigrlyceride levels remained high, . The TBARS level elevated in group B but remained unchanged in groups A and C. In groups B and C, the threshold of ABR increased mildly. The cholesterol load led to injuries in the endothelium of the vasculature dominating the cochlea. This is followed by an anormaly affecting cochlear lipid metabolism that results in ultrastructural changes of cochleal nerve fiber under spiral limbus, stria vascularis and inner hair cell and outer hair cell of Corti's organ. However, in the Vit. E-added hyperlipid diet group, blood vessel and cell injuries seemed to have been inhibited by the antioxidation activity of Vit. E.