Zhong Shixun, Liu Zhaohua
Department of Otorhinolaryngology and Head-Neck Surgery, Daping Hospital, Third Military Medical University, Chongqing 400042, China.
Zhonghua Er Bi Yan Hou Ke Za Zhi. 2002 Oct;37(5):324-8.
To investigate the effect and its mechanism of gentamicin(GM) on melanin in stria vascularis of guinea pig.
The differences of auditory thresholds between pigmented and albino guinea pigs, given GM of 150 mg/kg for 7 days, were studied. Moreover, the content of melanosomes, activity of tyrosinase and expression of proliferating cell nuclear antigen(PCNA) in intermediate cells of stria vascularis in gentamicin-treated pigmented guinea pigs were compared with those in control animals by electron microscope and immunohistochemistry, respectively.
After gentamicin exposure, the auditory thresholds of all animals increased significantly (P < 0.001), whereas threshold shifts averaged across all frequencies of pigmented animals were much less than those of the albinos(P < 0.001). The number of melanosomes of each examined area (300 microns 2) in intermediate cells was obviously increased from 19.83 +/- 2.74 to 58.33 +/- 16.22. The ratio of tyrosinase reaction products area to the total measured area was significantly increased from 1.65% +/- 0.40% to 3.45% +/- 0.41% after gentamicin exposure. However, the numbers of positive intermediate cells expressing PCNA were 14.08 +/- 2.76 and 13.58 +/- 2.09 before and after gentamicin treatment, respectively. But there was no statistically significant difference between them (P > 0.05).
The increase of content of melanin in stria vascularis after GM exposure does not result from the change of proliferating activity of melanocytes, but from the enhanced tyrosinase activity. Melanins in stria vascularis may possess the ability to protect the inner ear from ototoxicity of gentamicin.
探讨庆大霉素（GM）对豚鼠血管纹黑色素的影响及其机制。
研究给予150mg/kg GM共7天的有色豚鼠和白化豚鼠之间的听阈差异。此外，分别通过电子显微镜和免疫组织化学方法，比较庆大霉素处理的有色豚鼠与对照动物血管纹中间细胞中黑素小体的含量、酪氨酸酶的活性以及增殖细胞核抗原（PCNA）的表达。
庆大霉素暴露后，所有动物的听阈均显著升高（P<0.001），而有色动物所有频率的平均听阈变化远小于白化动物（P<0.001）。中间细胞中每个检查区域（300平方微米）的黑素小体数量明显增加，从19.83±2.74增加到58.33±16.22。庆大霉素暴露后，酪氨酸酶反应产物面积与总测量面积的比值从1.65%±0.40%显著增加到3.45%±0.41%。然而，表达PCNA的阳性中间细胞数量在庆大霉素处理前后分别为14.08±2.76和13.58±2.09。但两者之间无统计学显著差异（P>0.05）。
GM暴露后血管纹中黑色素含量的增加并非源于黑素细胞增殖活性的改变，而是源于酪氨酸酶活性的增强。血管纹中的黑色素可能具有保护内耳免受庆大霉素耳毒性的能力。
