General effects of hyperosmolar agents on the endolymphatic sac

The effects of glycerol, urea and mannitol on the structure of the murine endolymphatic sac were investigated at various time intervals after their administration. Within 15 min after administration of glycerol and urea the lumen of the endolymphatic sac was partially collapsed and the density of its contents was increased. At the same time many light epithelial cells displayed abundant intracytoplasmic granules containing floccular and/or lamellar material. A similar type of material was observed in the lumen in close proximity to these cells. This suggested that macromolecular substances were secreted into the endolymphatic sac lumen from these cells. Mannitol induced similar changes, though less pronounced. It is proposed that the changes in the endolymphatic sac following systemic administration of hyperosmolar substances reflect an ability of the endolymphatic sac to compensate for endolymphatic volume and pressure changes caused by these agents.