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 mormotensives had higher maximum cochlear potential-intensity values compared with the hypertensives: 1,000 Hz (P<0.005), 5,000 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), 1,000 Hz (P<0.025), and 2,000 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.