The difference in endolymphatic hydrostatic pressure elevation induced by isoproterenol between the ampulla and the cochlea.

<bold>Objective: </bold>The purpose of the study was to investigate the difference in the responses of endolymphatic hydrostatic pressure to isoproterenol, β-adrenergic receptor agonist, between pars superior and pars inferior.<bold>Methods: </bold>The hydrostatic pressure of endolymph and perilymph and endolymphatic potential in the ampulla and the cochlea during the intravenous administration of isoproterenol were recorded using a servo-null system in guinea pigs.<bold>Results: </bold>The hydrostatic pressure of endolymph and perilymph in the ampulla and cochlea was similar in magnitude. Isoproterenol significantly increased hydrostatic pressure of ampullar and cochlear endolymph and perilymph with no change in the ampullar endolymphatic potential and endocochlear potential, respectively. The isoproterenol-induced maximum change of endolymphatic hydrostatic pressure in ampulla was significantly (p<0.01) smaller than that in the cochlea. In ears with an obstructed endolymphatic sac, the action of isoproterenol on endolymphatic hydrostatic pressure in the ampulla disappeared like that in the cochlea.<bold>Conclusion: </bold>Isoproterenol elevates endolymphatic hydrostatic pressure in different manner between the vestibule and the cochlea. [ABSTRACT FROM AUTHOR]