Localization of peptides that regulate inner ear fluid in the rat

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The anti-diuretic hormone, vasopressin, has been shown to be important in regulating inner ear fluid. The diuretic hormone, CNP, and its receptor, ANP-B receptor, may also function in the regulation of inner ear fluid. To determine whether vasopressin directly affects the fluid level, we infused this hormone to rat and assay of V2-AVP receptor mRNA by semiquantitative RT-PCR demonstrated a significantly lower level of this transcript in vasopressin-infused animals than in saline-infused animals. The levels of CNP and ANP-B receptors mRNA, however, were the same in both groups of rats. Localization of vasopressin V2 receptor was identified by insitu hybridization. And we chronically infused this hormone to rats and examined them for morphological signs of endolymphatic hydrops. Enlargement of the scala media area was observed in the vasopressin-infused rats. The results suggest that high plasma levels of vasopressin may be a principal causal factor of endolymphatic hydrops in Meniere's disease, perhaps by down-regulating the number of vasopressin receptors.