Role of NO on the cochlear blood flow regulation

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Endothelial nitric oxide synthase (eNOS) is known to be present in the endothelial cells of various blood vessels of the body, and produces nitric oxide (NO) which acts as on the vascular smooth muscle to dilate the vessels under physiologic conditions. Thus it plays an important role in the maintenance of vascular tone throughout the vascular tree. Previous studies have demonstrated histochemically and Immunohisto-chemically the presence of eNOS and its second messenger system (soluble guanylyl cyclase and cyclic GMP) in several areas of guinea pig and rat cochlea. We conducted an experiment using rats to observe the changes in cochlear blood flow (CoBF) after the administration of N-nitro-L-arginjne-methyl ester, L-NAME, an inhibitor of NOS employing a laser-Doppler flowmeter. Intravenous infusion or round window application of L-NAME produced a dose-dependent depression of CoBF. Infusion of L-arginine,which is a substrate of NO partially reversed the CoBF decrease caused by L-NAME. … More Such change in blood might have occurred in the blood flow of abdominal wall (AbBF) and auricular blood flow (AuBF), But the changes of AbBF and AuBF after intravenous infusion of L-NAME were less than the change of CoBF. NO could be involved in the reguiation of cochlear blood circulation in at least two sites ; capillaries of spiral ligament and spirai prominence, and the spirai modiolar artery. Since the vascular tone of spiral modiolar artery is one of the crucial factors in regulating cochlear blood flow and tissue oxygenation, control of the diameter at some portion of the spiral modiolar artery is thought to be an energetically effective means for blood flow regulation of downstream capililaries, There may exist the NO/soluble guanylate cyclase/cyclic GMP system thus functioning as a resistance vessel. Considering the results, these activities of the system in the cochleal vasculature may be higher compared with those in cutaneous vasculatures of the abdominal wall and auricle. From the findings of that study, they proposed that NOS is present in the cochlear vasculature, where NO is produced to play a pivotal role in the regulation of vascular tone. Less