Effects of Experimental Acute Hypertension on the Blood-Labyrinthine Barrier

Abstract

With intraperitoneal injection of 0.16mg/kg methoxamine hydrochloride, experimental acute hypertension was made in guinea pig. Blood pressure was measured with a physiological pressure transducer. The initial mean blood pressure was 50-60mmHg and methoxamine caused a rapid increase of 50-60mmHg in about 15-20 minutes.For the first experiment, Kanamycin was used as a tracer. Four hundred mg/kg Kanamycin was injected intraperitoneally, and 20min. after injection, acute hypertension was created.Inner ear fluids were collected with micro-glass capillaries 10min., 40min., and 3 hours 40min. after inducing acute hypertension. Kanamycin concentrations in the inner ear fluids were measured with the bioassay technique.The results showed that Kanamycin went into the inner ear fluids rapidly at a higher dose with acute hypertension, and excretion from inner ear fluids were rapid compared with the normal group. This result indicates that the permiability of Kanamycin through the blood-labyrinthine barrier seems to be increased by acute hypertension.The ion concentrations of the inner ear fluids under the effect of acute hypertension were measured with an atomic absorption spectro photometer (Japan Jarrell Ash AA 855). Fifteen minutes after injection of methoxamine, the inner ear fluids were taken and K+ and Na+ ion concentrations were analysed. The results show that in the case of perilymph, the K+ ion concentration in the scala tympani was increased; the Na+ ion in the scala vestibuli was decreased; and in the endolymph, K+ was decreased and Na+ was increased.From these two experiments, we concluded that the function of the blood-labyrinthine barrier was affected by acute hypertension and the ion concentrations in the inner ear fluids were also changed.Because of the relationship between the perilymph and endolymph, which changes of ion concentrations are primary is not known and the meaning of these changes is not clear.The osmotic pressure between the endolymph and perilymph may be changed and if these unbalances in the ion concentrations are continued, histological and functional disturbances of the inner ear can occur.