Abstract
A histopathological feature of Meniere's disease is endolymphatic hydrops. Furthermore, a human temporal bone study has revealed that the endolymphatic sac showed fibrosis and/or hypoplasia in a patient with Meniere's disease. Based on this histological finding, malfunction of the endolymphatic sac may cause endolymphatic hydrops. However, it is impossible to explain the fluctuation of Meniere's symptoms with this retention hydrops, so the mechanisms underlying the endolymphatic hydrops of Meniere's diseases is still unclear. Clinically, it is well known that stress aggravates the condition of Meniere's disease. It seems to be that there are some relationships between stress and endolymphatic hydrops. Endolymphatic hydrops could be taken as malfunction of water homeostasis in the inner ear. If this is the case, one of stress hormones, vasopressin, could regulate water homeostasis in the inner ear. Actually, plasma vasopressin levels have been reported as elevated in patients with endolymphatic hydrops including Meniere's disease. Experimentally, vasopressin type 2 receptor was expressed in the basal cell of the stria vascularis. Moreover, the water channel of aquaporin (AQP) 2, the relocalization of which is regulated by vasopressin, was also expressed in the stria vascularis. Further, other AQPs were also expressed in the stria vascularis. To investigate the effect of vasopressin on the inner ear, vasopressin was administered to rats or guinea pigs. Vasopressin induced enlargement of the intrastrial space and endolymphatic hydrops. These results indicate that vasopressin affects the stria vascularis and endolymphatic hydrops was induced as a consequence. The following is a summary. Basically, patients with Meniere's disease have malfunction of the endolymphatic sac with retention hydrops. If the patients are under stress, the secretion of vasopressin would increase. The increase of vasopressin level causes the enlargement of the endolymphatic hydrops. These conditions may induce the symptom of Meniere's disease. Based on these clinical and experimental results, we produced a new animal model for Meniere's disease with vestibular disorder.
