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

We present controlled laboratory studies of the spontaneously hypertensive rat which indicate that hypertension is an important pathophysiological risk factor in age-related hearing loss. Our 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 United States, in view of our results it is possible that its treatment and early diagnosis will benefit a significant number of people who would otherwise lose their hearing with advancing age. We compared the round window ac cochlear potential-sensitivity and -intensity functions in 10 female spontaneously hypertensive rats and 10 female normotensive Wistar-Kyoto control rats. The animals were all 12 months old and weighed between 170 and 250 g. The normotensives had higher maximum cochlear potential-intensity values compared with the hypertensives: 1,000 Hz (P less than 0.005), 5,000 Hz (P less than 0.005), and 10,000 Hz (P less than 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 less than 0.05), 200 Hz (P less than 0.10), 290 Hz (P less than 0.05), and 2,000 Hz (P less than 0.10). Blood pressure of the hypertensive group was significantly greater than that of the normotensive rats (P less than 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.