Effects of vasopressin on gene expression in rat inner ear

Vasopressin regulates water excretion from the kidney by increasing water permeability of the collecting duct as a hormone secreted from the posterior pituitary. A clinical study reported that plasma levels of arginine vasopressin were significantly higher in patients suffering from Meniere's disease. It was histologically confirmed that chronic administration of vasopressin induced endolymphatic hydrops in guinea pigs. However, the mechanism of endolymphatic hydrops induced by vasopressin is still unclear. We use cDNA microarray to study the effects of vasopressin on gene expression profiles in rat inner ear to elucidate the possible mechanism of the induced hydrolabyrinth. Wistar rats were intraperitoneally injected with 50 μg/kg arginine vasopressin once a day for one week. Hydrolabyrinth in rat inner ear induced by administration of vasopressin was detected by HE stain. The bullae were dissected out for total RNA extraction. cDNAs were synthesized by reverse transcription and labeled with Cyanine3 (Cy3) or Cyanine5 (Cy5). The BiostarR-40s cDNA microarray was hybridized with the above cDNAs and the changes of mRNA expression intensity were showed by data analysis. Furthermore, the changes of aquaporins expression level were measured by reverse transcription polymerase chain (RT-PCR). Endolymphatic hydrops were present in rats intraperitoneally injected with vasopressin. 226 known differentially expressed genes were screened out in rat inner ear induced by vasopressin injection. Of the 226 genes, 18 transcripts were increased by 5-fold or more, and 7 transcripts were decreased to 0.2-fold or less. Ten differentially expressed genes were identified that associate with cell signal transduction, 14 differentially expressed genes were identified that relate to ion transport, 7 differentially expressed genes were involved in vesicle-mediated transport, and 2 differentially expressed genes were aquaporin 2 (AQP2) and aquaporin 7 (AQP7). The expression level of AQP2 was significantly higher and AQP7 was significantly lower. These results suggest that there are obvious differences in gene expression profiles in inner ear between vasopressin injected rats and normal control rats. Vasopressin may disturb fluid homeostasis in inner ear by way of signal transduction, ion transport, vesicle-mediated transport and aquaporins. It is likely that up-regulated expression of AQP2 mRNA and down-regulated expression of AQP7 mRNA in the rat inner ear caused by vasopressin induce an increased production and a decreased absorption of endolymph, resulting in endolymphatic hydrops.