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C. K. Sheng, X. Zhu, J. Wallman; Insulin Thins Choroids and Increases Scleral GAG Synthesis in vitro. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1734. doi: https://doi.org/.
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Insulin and glucagon have opposite effects in many situations. For example, in chick eyes, insulin stimulates the proliferation of progenitor cells at the retinal margin, whereas glucagon reduces it (Fischer et al., 2002, 2005). Glucagon has been shown to reduce the effects of negative lenses and form deprivation on choroidal thickness and ocular elongation; whereas insulin has been shown to reduce the effects of positive lenses (Zhu et al., 2007). We asked whether these effects of insulin occur in vitro and whether they require the presence of the retinal pigment epithelium (RPE).
Eyes from 1-week-old chicks were hemisected and the retinas removed to make eye-cups. One eye-cup from each bird was incubated in L-15 medium containing insulin and the other eye-cup was incubated in plain L-15. Eye-cups with the RPE attached to the choroids were incubated in insulin at 6.4, 0.64, or 0.064 USP units/mL; those without the RPE were incubated in insulin at 6.4 units/mL. Choroidal thickness was measured by A-scan ultrasound before and after 20 hours of incubation; synthesis of scleral GAGs was studied after 44 hours of incubation.
In eye-cups with the RPE attached, insulin caused a dose-dependent thinning of the choroids (r2=0.4; p<0.001). At doses of 6.4 and 0.64 units/mL, the eye-cups with insulin thinned significantly more than the untreated eye-cups (-60 ± 6 µm and -41 ± 13 µm, respectively [mean ± SEM]). In eye-cups without the RPE, insulin thinned the choroids significantly, but less than in eye-cups with the RPE (-33 ± 19 µm). Scleral GAG synthesis in the insulin treated eye-cups with RPE attached was nearly twice as high as their controls at all the three concentrations (1.99 ± 0.25, 1.76 ± 0.3, 1.66 ± 0.3 at 6.4, 0.64, 0.064 units/mL).
In vitro, as in vivo, insulin thins the choroid and increases the synthesis of scleral GAGs. Its effect on the choroid is stronger when the RPE is present.
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