Fluids from various inner ear compartments were taken from 77 ears of 70 normal, healthy cats and were analyzed for glucose concentration by the microchemical technique employing the hexokinase method. Perilymph of the scala vestibuli, perilymph of the scala tympani and C.S.F. had almost identical concentrations of glucose with the values approximately 80 mg/100 ml. Glucose concentrations of each fluid showed the significant relationship with serum glucose level except that of utricular and cochlear endolymph. Utricular endolymph glucose level was found to be lower (41.9 mg/100 ml) than the above three fluids and higher than cochlear endolymph (11.2 mg/100 ml). The significant difference of glucose concentration found between cochlear and utricular endolymph in the present study is further support for the independent nature of each endolymphatic compartment.

Sodium, potassium and glucose were analyzed in serum, C.S.F. and inner ear fluids up to five hours after intravenous regular insulin (30 units/kg). Sodium, potassium and glucose concentrations were unchanged in both cochlear and utricular endolymph during hypoglycemia. In contrast glucose concentrations in C.S.F., scala tympani perilymph, and scala vestibuli perilymph began to decrease at 90 minutes after regular insulin infusion and fell to their lowest levels in the period during 180 to 300 minutes after the infusion. A significant decrease of potassium concentration was found first in serum and later in the C.S.F., scala vestibuli, and scala tympani perilymph. For five hours after insulin infusion there is no significant change in cochlear microphonics during hypoglycemia (20 mg percent).