| Objective: To study the mechanism of retinal light injury and the protective effects of estrogen on light-induced photoreceptor degeneration. Methods: Thirty female Sprague-Dawley rats brought into treated group were randomly divided into three groups: ovariectomized (OVX), sham-ovariectomized, ovariectomized and estrogen (E2) replacement groups (OVX+ E2). Four rats which were not treated were brought into control group.After one week of operation, in the OVX+E2 group, E2 (50μg/kg) was subcutaneousely injected once on alternate days, and serum estrogen concentration of rats in the treated group were tested by cheniluminescence way.All of rats in the treated group were exposured to 12-hour light: 12-hour dark cyclic white fluorescent light for fourteen days two weeks postoperation. The light intensities were 600±35.41ux. They were given 24 hours dark-adaptation after duration of exposure, the flash electroretinogram (f-ERG) including scotopic blue ERG and scotopic white ERG was tested, then the amplitude of b wave were analyzed. Afterwards, all the rats in each group were anesthetized with 5% chloral hydrate, and the eyes were extracted to make paraffin sections, stained by HE. Retina was observed under light microscopy and thickness of outer nuclear layer was measured. TUNEL method was used to evaluate positive apoptosis cells on outer nuclear layer. The expression of Nitric oxide synthase (NOS) in retinal cells was investigatedby immunohistochemistry together with image analysis method.Results: Serum estrogen concentrations of rats in the OVX group were45.99±10.41pmol/L, which of sham-OVX group and 0VX+E2 were 136.04±51.69 pmol/L, 153.64±29.34 pmol/L respectively. Serum estrogen concentrations of rats in the OVX group were significantly less than those of the others (p=0.000). The amplitudes of b wave of scotopic blue ERG and scotopic white ERG were 24.30±8.44μv, 38.54+ 11.86μv, respectively in the OVX group, those of sham-OVX group and OVX+E2 were 40.05 ± 10.59μv, 66.61 ± 16.97μv and 37.52+10.01 μv, 62.74+ 17.89μv respectively. Differences between OVX group and the others were significant. Normal rats have clear layers of retinal structures. The outer nuclear layer(ONL)arranged orderly and regularly. Nuclear chromatin of photoreceptors had even density. No positive marked cell was found when we distinguished apoptotic cells by TUNEL method. In the treated group, the thickness of ONL became thinner, but the thickness of OVX was obviously thinner than those of the others. Positive marked cells in the OVX group were 27.53 + 6.95/1000μm2, which of sham-OVX and OVX+E2 were 16.15 + 5.44/1000μm2 , 17.49 + 5.97/1000μm2, respectively; the differences between the OVX group and the others were significant (q=4.1370, p=0.000; q=3.6497, p=0.001). The values of integral optical density in the OVX group were 0.3675 + 0.06621, Which of OVX+E2 group and sham-OVX group were 0.2941 +0.03498, 0.3027 + 0.03217 respectively. The NOS levels in the OVX group were evidently higher than those in the OVX+E2 group and in the sham-OVX group (q=3.4885, p=0.002; q=3.0798, p=0.005).Conclusions: Moderate and low intensities of cyclic light may inducephotorecepter degeneration and damage retina.Estrogen can restrain photorecepter apoptosis by control Nitrogen monoxide synthase and relieve retinal light injury.
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