[The effects of cerebral metabolic activator and vasodilator on cochlear blood flow]

We investigated the effects of intravenous injections of bifemelane hydrochloride, nicergoline and trapidil on cochlear blood flow (CoBF) and cerebral blood flow (CBF) using laser Doppler flowmetry, while monitoring arterial blood pressure (BP), in 40 guinea pigs. Each animal was anesthetized with 40mg/kg of intraperitoneal pentobarbital sodium. After tracheotomy, the animals were artificially ventilated with a respirator. The left middle ear was approached ventrally and the bulla was opened. The middle ear mucosa over the bony cochlea was removed. The tip of the probe was placed on the curvature of the basal or second turn of the cochlea, connecting it to a laser Doppler flowmeter. For the measurement of CBF, part of the parietal bone was exposed. The tip of the probe connected to a laser Doppler flowmeter was placed over the area. A catheter was inserted into the right carotid artery and connected to a pressure transducer. Another catheter for drug administration was cannulated via the jugular vein. Of 40 animals, 22 animals were given bifemelane hydrochloride, 10 animals received nicergoline and 8 animals were given trapidil. The drugs were administered in increasing concentrations, by intravenous injection, for 1 min at intervals of about 20 min in a volume equivalent to 1ml/kg. Asphyxia was induced by stopping the respirator for 2min before and after the experiment. CoBF, CBF and BP were simultaneously recorded. CoBF, CBF and BP rose after bifemelane hydrochloride administration. Nicergoline injection slightly decreased BP, but CoBF and CBF were unchanged. Trapidil injection slightly decreased BP and CBF, but increased CoBF at some concentrations. The high concentration injections of all drugs resulted in increases in normalized cochlear blood flow (CoBF/BP; nCoBF). After asphyxia, CoBF, nCoBF, CBF and BP tended to reach high levels in guinea pigs pretreated with bifemelane hydrochloride, as compared with untreated animals. While administration of nicergoline and trapidil exerted no influence on the changes caused by asphyxia in CoBF, nCoBF, CBF and BP. In this experiment, BP, CoBF and CBF responded in various ways to the three drugs tested, but analysis of nCoBF indicated that these drugs had a vasodilatory effect in the cochlea.