Effect of Furosemide upon Cochlea with Endolymphatic Hydrops

Abstract

Endolymphatic hydrops was induced in albino guinea pigs by obliteration of the endolymphatic sac and duct. High doses of furosemide (FUR) (50 or 80 mg/kg) were injected intravenously in the 3rd, 6th, 12th or 24th postoperative week and the effect on the cochlear endolymphatic potential (CEP) was examined in order to assess the functional capacity of the electrogenic pump in the stria vascularis. Low doses of FUR (5 or 10 mg/kg), which did not influence the CEP in normal or hydropic ears, were administered in the same way, and the input-output functions of the Ni induced by a click were monitored. The CEP was lower in the animals with endolymphaxic hydrops than in the normal controls and then tended to decrease gradually. When 50 mg/kg of FUR was given, the hydropic ears showed a greater depression of the CEP than the normal ears, indicating increased susceptibility to FUR in hydropic ears. Eighty mg/kg of FUR, which was enough to abolish almost all of the positive component of the CEP, reduced the CEP to -40 mV 12 weeks after surgery. This finding suggests that the negative K+ diffusion potential is normally maintained for at least 12 weeks postoperatively. The maximum recovery rate of the CEP after FUR injection (80 mg/kg) was significantly slower in the 24-week animals than in the other group, indicating more severe dysfunction of the strial electrogenic pump. In terms of the in-put-output functions of the Ni, no shift of the curves was observed up to 120 minutes after the administration of low doses of FUR in either the hydropic or the normal ears. It was concluded that the diuretic effect of FUR, could not improve the hearing of ears with endolymphatic hydrops.