Effects of electroacupuncture on cochlear morphology and expression of aquaporins in rats with AVP-induced endolymphatic hydrops

Objective: The objective of this study was to investigate the effects of EA on EH and the regulation of AQP2 and AQP7 protein expression in rats.Methods: Twenty-four rats were allocated randomly to four groups of blank group, EH group,EH+tolvaptan group and EH + EA group(n = 6 per group). EH rat model was established by intraperitoneally injection of arginine vasopressin(AVP). EA was administered at acupoints "Baihui(百会 GV 20)"and "Tinggong(听宫 SI 19)". Rats in the EH + tolvaptan group and EH+ EA group were treated with tolvaptan and EA, respectively, after EH establishment. Hematoxylin-eosin staining was used to measure the cochlear hydrops degree, and then the ratio of scala media(SM) area to SM + scala vestibuli(SV) area(R value) was calculated. Immunohistochemical method was used to observe AQP2/AQP7 protein expression in the rat cochlear lateral wall after treatment.Results: ①There was no endolymphatic hydrops in the blank group. Reissner' s membrane was extended markedly and bulged into SV in cochleae of the EH group and endolymphatic hydrops was noted. Statistical analysis revealed that R value in the EH group showed a significant increase compared with that in the blank group(0.42 ± 0.02 vs. 0.31 ± 0.05, P=0.000). The distension of Reissner's membrane was less obvious in the EH + tolvaptan group and EH + EA group when compared with the EH group. R value in the EH + tolvaptan group and the EH + EA group was significantly less than that in EH group(0.32±0.04 vs. 0.42 ± 0.02, =0.001;0.35 ± 0.05 vs. 0.42 ± 0.02, P=0.012). The degree of the hydrops in the EH + EA group was not different from that in the EH + tolvaptan group(0.35 ± 0.05 vs. 0.32 ±0.04,P= 1.000). ②The AQP2 protein expression in the rat cochlear lateral wall of EH group was significantly increased when compared with the blank group(12.74 ± 5.18 vs. 5.92 ± 1.52, P = 0.014). The AQP2 protein expression in the rat cochlear lateral wall of EH + tolvaptan group and EH + EA group were all lower than that of the EH group(6.52 ± 2.73 vs. 12.74 ± 5.18. P = 0.029;6.95 ± 3.10 vs. 12.74 ± 5.18, P = 0.047).The AQP2 protein expression in the rat cochlear lateral wall of EH + EA group was not different from that in the EH + tolvaptan group(6.95 ± 3.10 vs. 6.52 ± 2.73, P= 1.000).③The AQP7 protein expression in the rat cochlear lateral wall of EH group was significantly increased when compared with the blank group(30.32 ± 6.39 vs 16.64 ± 3.21, P=0.000). The AQP7 protein expression in the rat cochlear lateral wall of EH + tolvaptan group and EH + EA group were all lower than that of the EH group(18.32 ± 2.45 vs.30.32 ± 6.39, P= 0.001;19.54 ± 4.61 vs. 30.32 ± 6.39, P= 0.003). The AQP7 protein expression in the rat cochlear lateral wall of EH + EA group was not different from that in the EH + tolvaptan group(19.54 ±4.61 vs. 18.32 ± 2.45, P= 1.000).Conclusions: These results indicate that repeated EA stimulation exerted the same effects as tolvaptan application on AQPs levels and subsequent aquaretic effects. And dehydrating effect of EA on the inner ear might be associated with its down-regulation of both AQP2 and AQP7 protein expression, thereby provide a potential molecular mechanism involved in the treatment of Meniere's disease by EA.