Ultrastructure of the endolymphatic sac in two-phase endolymphatic hydropsin the guinea pig

Two-phase endolymphatic hydrops is a subtle experimental model for Meniere' s disease. Chronic dysfunction of the endolymphatic sac, induced by dissect ion of the most distal part without causing damage to the intermediate part , is combined with increased endolymph production induced by administration of aldosterone which stimulates the Na/K-ATPase in the stria vascularis. A transmission electron microscopic study was performed on the endolymphatic sacs of four groups of guinea pig cochleas: controls; non-operated aldoste rone-treated cochleas: operated (dissection of the endolymphatic sac) cochl eas; operated and aldosterone-treated cochleas. Light and electron microsco py showed a normal morphology in the controls. Aldosterone treatment had no visible effect. Dissected ears revealed severe deviations. The epithelium of the intermediate sac was low, showed dilated lateral intercellular space s indicating elevated fluid transport and displayed serious degenerative pr ocesses. Distally, the endolymphatic sac was completely blocked by newly fo rmed bone. Additional aldosterone treatment had no cumulative effect on the dissected ears.