[Effect and its mechanism of gentamicin on melanin in stria vascularis of guinea pig].
OBJECTIVE
To investigate the effect and its mechanism of gentamicin(GM) on melanin in stria vascularis of guinea pig.


METHODS
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.


RESULTS
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).


CONCLUSIONS
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.
Zhong
Shixun
S
Department of Otorhinolaryngology and Head-Neck Surgery, Daping Hospital, Third Military Medical University, Chongqing 400042, China. a68705648@online.cq.cn
Liu
Zhaohua
Z
D000818:Animals; D001309:Auditory Threshold; D005260:Female; D005839:Gentamicins / Q000494:pharmacology*; D006168:Guinea Pigs; D008297:Male; D008543:Melanins / Q000378:metabolism*; D008544:Melanocytes / Q000378:metabolism; D020460:Melanosomes / Q000378:metabolism; D014442:Monophenol Monooxygenase / Q000378:metabolism; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism; D013316:Stria Vascularis / Q000187:drug effects* / Q000378:metabolism
D005839:Gentamicins; D008543:Melanins; D018809:Proliferating Cell Nuclear Antigen; D014442:Monophenol Monooxygenase