Spontaneous genetic hypertension in the rat and its relationship to reduced ac cochlear potentials: implications for preservation of human hearing.

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Abstract
Controlled laboratory studies of the spontaneously hypertensive rat are presented which indicate that hypertension is an important pathophysiological risk factor in age-related hearing loss. These results are in concert with previous retrospective clinical studies that pointed to this possibility in man. Hypertension as a risk factor for hearing loss is within the bounds of known measures of diagnosis, treatment and even prevention, with monitoring early in life. Because hypertension is such a major public health problem in the USA, its treatment and early diagnosis will benefit a significant number of people who would otherwise lose their hearing with advancing age. The round window AC cochlear potential-sensitivity and -intensity functions were compared in 10 female spontaneously hypertensive rats and 10 female normotensive Wistar-Kyoto control rats. The animals were all 12 mo. old and weighed from 170-250 g. The normotensives had higher maximum cochlear potential-intensity values compared with the hypertensives: 1000 Hz (P < 0.005), 5000 Hz (P < 0.005), and 10,000 Hz (P < 0.01). One-microvolt isopotential cochlear potentials for the low frequencies of the normotensives showed greater sensitivity than those of the hypertensives: 100 Hz (P < 0.05), 200 Hz (P < 0.10), 290 Hz (P < 0.05), 500 Hz (P < 0.005), 700 Hz (P < 0.12), 1000 Hz (P < 0.025) and 2000 Hz (P < 0.10). Blood pressure of the hypertensive group was significantly greater than that of the normotensive rats (P < 0.001). The hearts and aortas of the hypertensive group were hypertrophied. Autonomic imbalance, platelet aggregation, decreased arterioles and natriuretic hormone were discussed as possible etiologies for the measured sensory hearing loss.