Improvement in inner ear blood flow by nitric oxide following experimentally induced cochlear thrombosis in anesthetized guinea pigs

The nitric oxide (NO) donor sodium nitroprusside (SNP) applied to the round window membrane has recently been found to increase cochlear blood flow (CoBF) in normal guinea pigs and in normal and presbyacusic mice. This study examined the effect of topical applications of SNP on experimentally impaired CoBF in anesthetized guinea pigs. Small (3 μl) portions of 3% SNP were applied to the round window niche of both normal and thrombosed cochleas. Local vascular impairment was produced by ferromagnetic thrombosis of cochlear blood vessels and the microcirculation measured using laser Doppler flowmetry. Ferromagnetic thrombosis resulted in a mean decrease of CoBF to 52% of baseline. There was a clear improvement in mean CoBF to 84% of baseline by the topical application of SNP that depended on the degree of ischemic damage produced. Under neuroleptanalgesia and ketamine-xylazine anesthesia, significant increases in CoBF were measured in normal ears as well as in the thrombosed ones. However, several SNP applications were needed to improve the impaired CoBF, while a single portion was sufficient in the normal cochlea to cause a drastic increase in mean CoBF to 234% of baseline. In urethane-anesthetized animals, no flow increase was found despite repeated drug administration. Careful evaluation of the laser Doppler signals was necessary to accurately determine the concentrations of the moving blood cells and their mean velocities. Received: 8 August 1997 / Accepted: 11 February 1998