Abstract
Pitressin is one of the hormones of the posterior lobe of the pituitary gland. It is known that pitressin acts to promote the reabsorption of the water and sodium ion in the distal kidney tubule. The stria vascularis resembles the kidney tubule histologically and it is well known that diuretics cause an increase in the concentration of sodium in the endolymph and a decrease of the concentration of potassium in the endolymph. The effect of pitressin on the cochlear microphonics (CM) was studied by means of differential electrode technics. The following results were obtained.
1. With the injection of 0.4 unit/kg of pitressin, the CM decreased gradually to 76.3% of the initial value within 30 minutes, to 64.3% within 1 hour and to 48.0% within 3 hours.
2. With the injection of 8 unit/kg of pitressin, the CM rapidly decreased to 46.7% of the initial value within 1 hour and maintained the same value for over 4 hours.
Pitressin caused a depression of the CM. It would be due to the decrease in the concentration of sodium in the endolymph by promoting the reabsorption of the sodium ion in the stria vascularis and the increase in the volume and pressure of the endolymph and perilymph, bacause the CM is easily affected by the ionic changes in the endolymph and perilymph.
