Cochlear blood flow and labyrinthine pressure: effects of glycerol on the inner ear

Changes in cochlear blood circulation (CoBC) and perilymphatic pressure (Pp) after administration of physiological saline and 50% glycerol (12 ml/kg) were measured simultaneously in guinea pigs to examine the influence of glycerol on CoBC and Pp. The CoBC was measured by the laser-Doppler method. Although neither CoBC nor Pp changed after administration of physiological saline, glycerol produced a marked increase in CoBC and a slight decrease in Pp in 11 of 15 animals. However, the increase in CoBC was transient; CoBC reached a peak as soon as 30 min after glycerol administration and then returned rapidly to its initial value within 1 h after administration, although the Pp was still decreasing. Therefore, the response of CoBC to glycerol does not seem to be directly related to hyperosmolarity due to glycerol administration.