CONCLUSIONS: 11beta-Hydroxysteroid dehydrogenase type 2 (11bHSD-2) enables aldosterone to bind to mineralocorticoid receptors (MRs) selectively by converting cortisol (corticosterone) into inactive metabolites. Its expression in the endolymphatic sac (ES) suggests that aldosterone may selectively act on the ES through its binding to MRs by the action of 11betaHSD-2, and supports the notion that ES is an aldosterone target organ. We propose that 11betaHSD-2 is a dominant isoform of 11betaHSDs in the ES, and the ES (especially the intermediate portion of the ES) may be the main aldosterone target in the inner ear. OBJECTIVE: The purpose of this study was to examine 11bHSD isoform expression in the rat inner ear, mainly 11betaHSD-2 in the ES. MATERIALS AND METHODS: In the ES and whole cochlea, 11betaHSDs were examined by RT-PCR using highly specific ES RNA by laser capture microdissection. In addition, 11betaHSD-2 localization in the rat ES was determined by immunohistochemistry. RESULTS: RT-PCR demonstrated 11betaHSD-2 expressed in the rat ES. In addition, its localization was observed mainly in the intermediate portion and a faint immune positive signal was observed in other parts of the ES. In contrast, 11bHSD-1 was undetectable in the ES by RT-PCR. Both types of 11betaHSDs were expressed in rat cochlea.
CONCLUSIONS:11beta-Hydroxysteroid dehydrogenase type 2 (11bHSD-2) enables aldosterone to bind to mineralocorticoid receptors (MRs) selectively by converting cortisol (corticosterone) into inactive metabolites. Its expression in the endolymphatic sac (ES) suggests that aldosterone may selectively act on the ES through its binding to MRs by the action of 11betaHSD-2, and supports the notion that ES is an aldosterone target organ. We propose that 11betaHSD-2 is a dominant isoform of 11betaHSDs in the ES, and the ES (especially the intermediate portion of the ES) may be the main aldosterone target in the inner ear. OBJECTIVE: The purpose of this study was to examine 11bHSD isoform expression in the rat inner ear, mainly 11betaHSD-2 in the ES. MATERIALS AND METHODS: In the ES and whole cochlea, 11betaHSDs were examined by RT-PCR using highly specific ES RNA by laser capture microdissection. In addition, 11betaHSD-2 localization in the rat ES was determined by immunohistochemistry. RESULTS: RT-PCR demonstrated 11betaHSD-2 expressed in the rat ES. In addition, its localization was observed mainly in the intermediate portion and a faint immune positive signal was observed in other parts of the ES. In contrast, 11bHSD-1 was undetectable in the ES by RT-PCR. Both types of 11betaHSDs were expressed in rat cochlea.