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C. K. Sheng, X. Zhu, J. Wallman; Insulin Acts on RPE to Thin Chick Choroid in vitro. Invest. Ophthalmol. Vis. Sci. 2009;50(13):3852.
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In chick eyes, exogenous insulin counters the effect of positive lenses by thinning the choroids and increasing ocular growth (Zhu et al., 2008; Feldkaemper 2008). In eye-cups without the retina, insulin reduces the choroidal thickness and increases the synthesis of scleral glycosaminoglycans (GAGs) (Sheng et al., ARVO 2008). This effect of insulin on thinning the choroid in eye-cups was significant only when the retinal pigment epithelium (RPE) was left on the choroids. To confirm a role of RPE in the action of insulin on the choroid, we studied the effect of adding transplanted RPE into eye-cups made without the RPE on choroidal thickness.
Eye-cups with the retina removed were made from 1-week-old chicks. RPE was obtained from donor eye-cups after incubation with 1mM EDTA in PBS at 37 ºC for 2 hours. Of each pair of recipient eye-cups from one bird, one received the RPE from either one or two donor eye-cups; the other received no RPE. Pairs were incubated in L-15 medium either with or without 37µM of insulin. Choroidal thickness was measured by A-scan ultrasound before and after 20 hours of incubation.
The choroidal thickening that occurs in vitro is reduced by insulin significantly more in eye-cups with the transplanted RPE than in the control eye-cups without the RPE. This thinning effect of insulin was even stronger in the eye-cups to which the RPE from two donor eyes had been added than those with RPE from one donor eye. Specifically, the average choroidal thickening was 61µm less in eye-cups with the transplanted RPE from one donor than their controls without RPE (26µm vs. 87µm; p<0.01 paired Student’s t-test; n=12) and 95µm less in eye-cups with RPE transplanted from two donors compared with their controls (-5µm vs. 90µm: p<0.01; n=7). In eye-cups incubated without insulin, choroids thickened about the same in eye-cups with or without the transplanted RPE (98µm vs. 84µm; n=4).
The finding that insulin exerts a greater effect on the choroid when transplanted RPE is present implies that insulin (or IGF-1) may act on the RPE to cause changes in choroidal thickness and perhaps in ocular growth.
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