An experimental study on auditory dysfunction associated with hyperlipoproteinemia.

Some clinical datum concerning the relationship between hyperlipoproteinemia and sensori-neural hearing loss have been reported. However, definite histopathological evidence causing hearing loss has not yet been clarified.Using 80 guinea pigs administrated hyperlipid diet (cholesterol 2.5%, bile acid 0.25%, cattle fat 7.5%) for 3 months, auditory dysfunction and histopathological changes in the coch-leae were studied. The results obtained were as follows:1. Biochemical findings of the sera showed hyperlipoproteinemia and liver dysfunction (fatty liver). Diabetes and renal dysfunction were not observed. Phenotype of hyperlipoproteinemia was Type IIa or Type IIb in all the animals examined. This hyperlipoproteinemic condition returned to a normal level after 3 months of breeding with a normal standard diet.2. Auditory dysfunction, the threthold change of auditory brainstem response (ABR), was mild. Forty per cent of the experimental animals showed increased threthold of ABR from 10 to 20 dB.3. Phospholipid staining by snake venom hospholipase digestive method revealed deposits of phospholipid in Corti's organ and the stria vascularis. They were especially intensive along the each cell membrane of the outer hair cells, of Hensen's cells, and of the inner piller cells, and in the marginal cells of the vascular stria. poradic losses of the outer hair cells were observed by succinic dehydrogenase staining. Electron microscopically, there were many protrusions toward the endolymphatic space on the surface of Corti's organ and on the marginal cells of the stria vascularis. Furthermore, vacuolar degeneration was observed in the basement membrane of the capillary of the stria vascularis. These morphological changes seemed to begin initially from the stria vascularis.In conclusion, mild auditory dysfunction associated with hyperlipoproteinemia was proved by the experimental animals breeded with hyperlipid diet. It is necessary, however, for getting more severe auditory damage to impose other factors besides hyperlipoproteinemia.