The effect of topical application of vasodilating agents on cochlear electrophysiology

The aim of this investigation was to study whether increased blood flow has beneficial effects on the ear or whether it is damaging to the auditory function, expressed as the auditory gross neural response. Four vasodilating agents were examined after topical application with respect to their influence on cochlear blood flow (CBF), blood pressure, and auditory function in the normal guinea pig. CBF was recorded with laser-Doppler. The drugs used were sodium nitroprusside, hydralazine, nicotinic acid and histamine. Sodium nitroprusside and hydralazine increased CBF and induced concentration dependent loss of auditory function. Neither nicotinic acid nor histamine had any effect on CBF. Nicotinic acid had varying effects: in some cases a negative influence on threshold shifts was seen, and in others a positive one. In most cases histamine caused improvement of the auditory function. The data indicate that topical administration of drugs to the inner ear is effective to influence both CBF and auditory function.