The effects of glycerol on vestibular function and the endolymphatic sac after pre-treatment with colchicine.

The endolymphatic sac (ES) is believed to absorb endolymph. Recent studies have suggested that the ES also has a secretory capacity, a function that may be related to the regulation of inner ear fluid volume and pressure. Other studies indicate that hyperosmolar substances, such as glycerol and urea, may initiate a secretion of glycoprotein into the ES. This function was suggested to be related to a regulatory function of the ES by which it can compensate for a decrease in endolymph pressure. In order to investigate this regulatory potential of the ES, the effect of glycerol on the ES was investigated with or without the presence of pharmacological inhibition of glycoprotein secretion through colchicine treatment. Animals treated in such a way showed marked signs of impaired inner ear function, including loss of postural control and loss of Preyer's reflex. Significant ultrastructural changes were noted in the endolymphatic sac suggesting a disturbed secretory activity. The results may indicate that the endolymphatic sac may actively respond to changes in endolymph homeostasis through secretion of macromolecular substances and that alterations in this secretion may lead to functional disturbances of the inner ear.