Lactate dehydrogenase (LDH) activity in the inner ear under acoustic overstimulation (author's transl)

Abstract

This paper gives the results of LDH activity of various tissue in the inner ear of a guinea pig, the organ of Corti organ, stria vascularis and perilyirphatic fluid under acoustic overstimulation. 47 normal guinea pigs, with good preyer reflex, were used for these experiments. These guinea pigs were exposed to white noise of 115 dB for various duration of time from 10 minutes to 72 hours. After acoustic stimulation, inner ears of animals were exposed by operation and perfused with LDH incubation. After animals were decapitated, the inner ear were fixed with Karnovsky's solution and embedded with paraplast. With the LDH staining method, aboundant deposits of reduced tetrazolium dyes were shown to be in the organ of Corti and stria vascularis. After exposure to noise for 60 minutes, almost all the formosan disappeared in both the organ of Corti and the stria vascularis. However, after exposure to noise for 15 hours, LDH activity increased in these areas again. As the next step of the experiment, the LDH activity in the organ of Corti and the stria vascularis were biochemically measured by socalled microbiochemieal technique. After decapitation of guinea pigs, their inner ears were put into 4°C physical NaCl solution. Using the surface preparation method, the organ of Corti and the stria vascularis of each turn were separately obtained and homegenated in minute glass tubes. After centrifusion, quantitative measurement of LDH activity and protein content was performed on the supernatant fluid. In normal guinea pigs, the organ of Corti and the stria vascularis showed almost the same level of LDH activity. The stria vascularis in the second turn showed the highest LDH activity, then first turn, third and the lowest activity in the fourth turn. After exposure to the noise for 60 minutes, the LDH activity of the stria vascularis decreased markedly in all turns and indicated the lowest level through the run. After exposure to noise for 15 hours, however, its activity increased to the highest level. After 72 hours, the LDH activity decreased again and returned to the normal level. The behaviour of LDH activity in the organ of Corti after acoustic overstimulation seemed to the same as it in stria vascularis. In perilymph, the LDH activity showed its highest level ( 5 times higher than normal level) on 15 hours exposure to the noise and then decreased gradually to the normal level.