Abstract
Pitressin is one of the hormons of the posterior pituitary. The authors reported that pitressin causes a depression of the cochlear microphonics. In this paper the effects of pitressin on CM modified by NaCl-crystals administered on the round window membrane were studied. The following results were obtained.
1. The placement of NaCl-crystals caused an overshoot of CM for 3 min. and 20 sec., a primary depression to 55.0% of the initial value within 15 min., a gradual recovery to 71.0% within 40 min. and then a gradual second depression.
2. The repeat placement of NaCl-crystals caused an overshoot of CM for 3 min. and 20 sec. and a gradual decrease to 140μV (46.7% of the initial value) within 20 min., to 80μV (26.7%of the initial value) within 50 min.
3. The NaCl-crystals were placed on the round window membrane 1 hour and 30 min. after injection of 0.4unit of pitressin. The placement of NaCl-crystals upon the round window membrane caused a gradual decrease of CM. The CM decreased to 226±33μV (75.3±11.0%) within 30 min., to 195±25μV (65.0±8.3%) within 1 hour and to 154±13μV (51.3±4.3%) within 2 hoursl As compared with the control, it is characteristic that the CM caused a gradual decrease without a recovery and the value of the CM at the 60th minute was less than the control.
4. The repeat NaCl-crystals were placed on the round window membrane 3 hours and 30 min. after injection of 0.4unit of pitressin. The placement of NaCl-crystals upon the round window membrane caused a mild depression of CM to 280μV within 10 min. and a rapid decrease to 220μV at the 55th min, to 190μV at the 60th min., and to 100μV at the 62th min. The CM decreased to 80μV within l hour and 30 min.
It was apparent that pitressin would cause an increase in the volume of the inner ear fluids, an increase of the hydrostatic pressure and the osmotic pressure and increase the impedance of the inner ear conductivity after the placement of NaClcrystals. Pitressin would also promote the reabsorption of sodium ion in the inner ear. According to these actions, the repeat placement of NaCl-crystals on the round window membrane with the premedication of 0.4unit of pitressin would prolong the rapid decrease of CM as compared with the control.
