Effect of vasodilating agents on cochlear blood flow under loud sound exposure.

Loud sound has been proved by means of laser Doppler flowmetry to decline cochlear blood flow. The purpose of this study was to investigate the effect of a vasodilating agent on cochlear blood flow under loud sound exposure, i.e. whether the drug can impede blood flow decrease or not. As a vasodilating agent, dilazep dihydrochloride in a dose of 5 mg/kg was used. This drug caused a stable and significant increase of cochlear blood flow when intravenously injected into guinea pigs. When guinea pigs were exposed to loud sound (120 dB SPL at 10 kHz) for 10 min, cochlear blood flow promptly declined at the onset of sound stimulation and promptly recovered at its cessation. Then, dilazep dihydrochloride 5 mg/kg was injected intravenously into the same animal and loud sound (120 dB SPL at 10 kHz) was exposed for 10 min. Dilazep did not fully block a prompt decline of cochlear blood flow. However, the blood flow level was kept much higher than at pre-injection level. This study shows that a vasodilating agent which normally enhances blood flow probably does not completely block the sound-induced drop response in cochlear blood flow.